Do you eat before or after your run?

Many long distance runners perform at least some of their long runs in a fasted state (for example before breakfast, without taking anything), hoping that this will teach their bodies to become more effective at using fats for energy production. Even though it is not sure that it helps on race day, studies have shown indeed that you become better at burning fats if you train your body to do so.

© Mikhail Shifrin | Dreamstime Stock Photos
© Mikhail Shifrin | Dreamstime Stock Photos

The next question is then: would it help you to lose weight? In other words: would you lose more fatty tissue when you exercise in a fasted state than after a meal? Brad Schoenfeld and his colleagues have investigated this and concluded that it does not seem to make a difference. They published their study in the Journal of the International Society of Sports Nutrition in November 2014.

They divided 24 young female volunteers in two groups. One group exercised in a fasted state and the other after consuming a meal replacement shake. They all worked out on a treadmill three times a week at 70% of their maximal heart rate and followed the same diet with the aim to slim down. The women who started by exercising had their shake immediately after the workout.

After four weeks, all the women had lost weight, but there were no differences between the groups concerning amount of weight lost, waist line, lean or fat mass.

The researchers therefore concluded that it does not matter whether you exercise before or after a meal.

Schoenfeld explains the findings by citing previous research showing that our bodies change what they use as fuel, depending on what is available. If you burn more fats for a while, you will use more carbohydrates later in the day, and you have therefore to look at much longer periods than just a few hours.

You might understand their findings better if you think about the First Law of Thermodynamics, which states that energy does not get destroyed or created, but only changes from one form into another. What matter is therefore to get rid of the excess energy, whatever the form it is in.

A study with a negative result?

It is true that reading a study with a negative result is always slightly disappointing, and that is why in the past they did not get published. It is great that this now changing, because it might avoid repeating the same studies over and over again and it might also help us (I hope!) to avoid doing useless things.

Disclaimer: this article is for general information only, and does not replace medical or coaching advice. It cannot be used to guide treatment or training. If you have any concerns or questions, you should talk to a qualified health provider.

References:

Schoenfeld B J, Aragon A A, Wilborn C D et al. Body composition changes associated with fasted versus non-fasted aerobic exercise. J Int Soc Sports Nutr. 2014; 11 (1):54.

Spriet L L. New insights into the interaction of carbohydrate and fat metabolism during exercise. Sports Med. 2014; 44( Suppl 1): 87.

Stannard S R. Ramadan and its effect on fuel selection during exercise and following exercise training. Asian J Sports Med. 2011; 2(3):127.

Van Proeyen K, Szlufcik K, Nielens H et al. Beneficial metabolic adaptations due to endurance exercise training in the fasted state. J Appl Physiol (1985). 2011; 110(1):236.

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Could exercising make you eat more?

Many people exercise in order to lose weight or to keep it under control, but does this make sense? It is beyond doubt that regular exercise will improve your health and well-being, but could it make you hungrier, and therefore make you eat more? If so, it would not make any difference for your waistline…

© Andre Maritz | Dreamstime Stock Photos
© Andre Maritz | Dreamstime Stock Photos

In the November 2014 issue of Nutrients, Stephanie Howe and her colleagues published a review article discussing what we know today about this subject. There are still plenty of questions left, especially concerning women, as most studies have been done on men. Studies on women are indeed much more difficult to conduct since oestrogen influences appetite, and researchers therefore have to control for the menstrual status.

Stephanie Howe and her colleagues explain how hormones influence our appetite, and how exercise influences these hormones. They then discuss several studies which have investigated this problem, and finally they look at the impact of diet.

They come to the conclusion that if you are sedentary, an acute bout of exercise is likely to make you overeat. However, as you become well-trained, your body becomes better and better at matching your energy intake with your expenditure.

They also note that as intense exercise suppresses your appetite more, you have to pay attention to what you are having after hard workouts: you could be tempted to eat too little or too late, which will delay your recovery.

Their article is free for all to read, and I will just try to make a summary in lay terms.

What determines your appetite?

Appetite is very complex and influenced by a long list of factors, such as gastric motility, the status of your energy reserves, temperature, dehydration… Your brain receives all this information via hormonal and neural signals, integrates them and then stimulates or suppresses your appetite.

The involved hormones can roughly be divided into two types: tonic circulating and episodic hormones.

The tonic circulating ones reflect your energy reserves and suppress your appetite when your energy stores are full, and are thus more involved with long term regulation. The best known ones are insulin and leptin.

The episodic hormones on the other hand are involved in short term appetite. Most of them are gut hormones and are released when you are eating or just before a meal. They suppress appetite, except for ghrelin, which makes you feel hungry. As their levels depend on what you are eating, it is easy to see why some diets make you feel fuller than others. Foods rich in fibres for example, will allow you to take in fewer calories without feeling hungry.

As mentioned earlier, oestrogen and progestogen also influence appetite, which explains why many women tend to gain weight during the menopause.

All these hormones act on the hypothalamus (an organ in your brain), which integrates the information and controls your appetite. Despite this sophisticated system, other factors, such as the sight and smell of food, cultural and social elements or the time of the day, also influence your desire to eat and can even override the hormonal influences.

Working Up Sweat (ID: 74747)
© Vlad | Dreamstime Stock Photos

Studying appetite

Researchers who want to study the influence of exercise on appetite therefore have to measure the amount of the appetite hormones in your blood as well as your desire to eat. The first can easily be done by a blood test, and the latter is often done using a visual analogue scale (VAS) or by measuring what the participants eat at a buffet in the research centre. A visual analogue scale typically consists of a series of numbered boxes (e.g. from 1 to 10), where the first and the last ones correspond to the extremes (e.g. “I’ve never been so hungry” and “I couldn’t eat anything at all”). You can then mark the box that corresponds best with how you are feeling.

Appetite hormones and exercise

A bout of aerobic exercise decreases your appetite by influencing your gut hormones. This effect is more pronounced in weight baring and more metabolic demanding exercise, such as running, than in non weight baring exercise.

Intense exercise influences the hormones more than moderate exercise. This suppression is only temporarily, but it can be enough to interfere with your next meal, and therefore with your recovery. This explains why it is so hard to eat anything solid after a race!

Resistance exercise on the other hand, does not seem to have an influence.

Are you really eating less?

It is not because your hormones are suppressing your appetite that you will eat less. As I am sure you know by experience, you can override your appetite if the food looks nice or if you believe you have good reasons to eat (e.g. I have spent a lot of calories, I need some comfort after all this hard work…).

© Ragne Kabanova | Dreamstime Stock Photos
© Ragne Kabanova | Dreamstime Stock Photos

Most studies looking into energy intake after exercise do so by measuring what the participants eat at a buffet offered by the researchers. This does not necessarily simulate real life and might therefore lead to false conclusions. Even so, there is evidence that trained people are able to match their energy intake to what they have spent, and can therefore maintain a healthy weight. Sedentary people however, are more likely to overeat after an acute bout of exercise.

Diet

Most athletes are health conscious and will choose a diet rich in fruit, vegetables, whole grains etc…Such a diet will contain fewer calories per volume than an unhealthy one. It will also make you feel full much earlier. For the vast majority of us this is excellent news, but the combination of a low calorie diet, intense exercise and appetite suppression can become a trap for some athletes. It can lead to a chronic negative energy balance, and is more often seen in women engaged in sports for which being lean is an advantage, such as long distance running. It can lead to menstrual disorders with all their complications: poor bone health, injury, illness…

Recovery

If you want to recover quickly, you have to refuel as soon as you can. This can be difficult if your appetite is suppressed. Other factors such as fatigue, dehydration, an elevated core body temperature or gastrointestinal problems can make things even trickier. A good recovery drink can help you out though, as drinking is much easier than eating.

 

Exercise and a family history of type 2 diabetes

© Kiankhoon | Dreamstime Stock Photos
© Kiankhoon | Dreamstime Stock Photos

Type 2 diabetes is more and more frequent in our Western world. It is probably the result of a complex and not- well-understood interaction of genes, lifestyle and obesity.

The disease starts with insulin resistance, which means that your tissues do not respond that well to stimulation by insulin. However, insulin is essential for the transfer of glucose from your blood into your tissues. As your tissues become resistant, you need more insulin to do the same job as before. If moreover the producing cells become dysfunctional, you will not be able to produce enough to keep your blood glucose levels normal and you will develop diabetes.

A family history of the disease is an important risk factor. Fortunately, you can lower your risk by exercising regularly. Working out will help you to normalise your glucose metabolism, as during exercise your muscles can take up glucose without insulin. It will also help you to keep your weight under control and reduce your risk of cardiovascular disease, which is diabetes’ major complication. Exercise is therefore a cornerstone of the prevention as well as of the treatment.

As exercise is so important for people at risk, the obvious question is: do people with and without a family history have different aptitudes for sport? To answer this, Antonio Bianco and his colleagues compared the aptitude for anaerobic performance of 33 elite athletes without a family history of type 2 diabetes with 13 elites with a family history.

The anaerobic metabolism is the pathway to produce energy without oxygen, as opposed to the aerobic metabolism. It is much quicker, but it is less economical than the aerobic metabolism, and your body will therefore use it for short, high intensity activities such as high intensity interval training and strength exercise.

The athletes performed squat jumps and a Wingate test*, which is the classical test to determine somebody’s peak anaerobic power.

As suspected, the athletes with a family history had a higher body mass than the others, but, surprisingly, their anaerobic performances were significantly better.

The majority of the studies showing the importance of regular workouts for diabetes used aerobic exercise. However, a mounting amount of evidence suggests that strength exercise is just as beneficial. If Bianco is right, his findings would be important for everybody who has a family history of type 2 diabetes, since it is likely that you will prefer an exercise discipline you are good at.

In other words: if you have a family history of type 2 diabetes, you might be better at sports that include shorter period of intense activity and/or power (e.g. most ball sports, gym work) than at endurance sports (e.g. distance running, walking). Maybe you would you therefore prefer them?

The most important thing is that you love your chosen form of exercise so much that you keep doing it!

*A Wingate test is performed on a specialised ergometer. After warming-up, the athlete starts pedalling as fast as possible. After three seconds the researcher adds a resistance corresponding to 75g/Kg of the athlete’s weight to the flywheel. The athlete continues to go as hard as possible for 30 seconds, and the researcher notes the peak power output.

Disclaimer: If you are new to exercising, please ask your doctor for advice first.This article is for general information only, and does not replace medical advice. It cannot be used to diagnose or guide treatment. If you have any concerns or questions, you should talk to a qualified health provider.

References and further reading:

A Bianco, F Pomara, M Raccuglia et al. The relationship between type 2 diabetes family history, body composition and blood basal glycemia in sedentary people. Acta Diabetol. 2014; 51(1): 79-84.

A Bianco, F Pomara, A Patti et al. The surprising influence of family history to type 2 diabetes on anaerobic performance of young male elite athletes. Springerplus. 2014; 3: 224. doi: 10.1186/2193-1801-3-224. eCollection 2014.

R Khardori, G T Griffing, B E Brenner et al. Type 2 Diabetes Mellitus. Medscape (Accessed on 5/10/2014).

R J Wood and E C O’Neill. Resistance training in type II diabetes mellitus: impact on areas of metabolic dysfunction in skeletal muscle and potential impact on bone. J Nutr Metab. 2012; doi:10.1155/2012/268197.  (Accessed on 5/10/2014).

Altitude training for endurance athletes

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© Ichtor | Dreamstime Stock Photos

There is no doubt that if you want to compete at altitude, you will first have to acclimatize to the lack of oxygen. If not, you will probably not perform as well as you could and you will certainly put your health at risk. However, does training at altitude help you to perform better at sea level? The jury is still out…

Lorenzo Pugliese and colleagues have published the latest article about this question in the September issue of the Journal of Sports Science & Medicine. It is an observational study of two elite endurance athletes, a race walker and a marathon runner, who used altitude training as part of their preparation for the Athens Olympic Games (2004). As both of them obtained gold medals, it must have worked for them, even though we do not know for sure what would have happened if they had stayed at sea level.

Even though altitude training is popular between endurance athletes and coaches, it is still controversial between scientists. In theory it should work of course: as the air pressure is lower at altitude, your body learns how to use oxygen more effectively, what then allows you to perform better when you are back at sea level. The best known effect is an increase in red blood cells, and thus in haemoglobin mass, although there are also adaptations at the level of the muscles and the mitochondria. This increase is triggered by the hormone erythropoietin or EPO, which is produced by the kidneys. However, some people produce less EPO than others and there are therefore important inter-individual differences between the effects of altitude on athletes.

Training hard and altitude

If you want to win endurance races, you need to be able to train at fast paces. Running fast for a long distance is difficult to do at altitude when you are not used to it, as your muscles need more oxygen than you can deliver to them. This is even more so for elite athletes, whose muscles are trained to perform at an optimal level. If you do not train intensively enough for a period of a time, your muscles become detrained, and anything you might have gained by improving your oxygen metabolism will be useless.

While you are acclimatizing, you will face some other problems:

  • Sleeping can be difficult as you are short of breath.
  • As soon as you arrive at altitude, your plasma volume (=the water part of your blood) will decrease, as your body wants to increase the red blood cell concentration and producing new red blood cells takes some time.
  • The air is colder and drier which can easily lead to dehydration.
  • As your muscles cannot extract as much oxygen from your blood as they do at sea level, your VO2max is in effect reduced. Running at the same speed as at sea level will therefore mean working at a higher level of your VO2max, which will feel harder.
  • You are more vulnerable to infections.

All these factors will make it difficult to train at the required level during the acclimatization. Once you are used to the altitude the situation will improve, but in the meanwhile you might have lost valuable time and your legs might have lost speed.

Athletes and coaches have therefore developed live-high-and-train-low camps, whereby they live at altitude and train at lower level. Alternatively, they might do live-low-and-train high camps, whereby they perform some of their sessions at altitude to have an additional training stimulus.

 Olga Vasilkova | Dreamstime Stock Photos
Olga Vasilkova | Dreamstime Stock Photos

Reasons for the controversy

Studies about altitude training contradict each other, whatever formula they use (live-high-and-train-high, live-high-and-train-low or live-low-and-train-high). It is of course possible that athletes and coaches have noted some benefits that are too small to be measured by scientists. As major championships are won or lost by seconds, such very small benefits can make a big difference indeed.

It more likely that the controversy is due to a lack of control groups: in a good study you would compare similar athletes doing the same training at altitude as at sea level, and you would take into account that some people do not react as well as others. In practise such a study is very difficult and expensive to conduct. To complicate matters even further, there could be a placebo effect, as most athletes believe that altitude training is beneficial.

Lorenzo Pugliese’s athletes followed a live-high-and-train-high program. However, they were able to train at the same running/walking pace as at sea level and, according to Pugliese, this is the reason why the camp worked so well for them. Both of them had extensive altitude training experience and that might well have been the reason for their success. Maybe a three week camp so now and then is simply not enough, and you might need to live for a long time at altitude to reap the benefits? This would explain why so many top endurance athletes are born and/or live at altitude. Bad news for all of us who live at sea level though…

References

D M Bailey and B Davies. Physiological implications of altitude training for endurance performance at sea level: a review. Br J Sports Med. 1997; 31:183-190.

L Pugliese, FR Serpiello, GP Millet et al. Training dairies during altitude training camp in two Olympic champions: an observational case study. J Sports Sci Med. 2014; 13(3):666-672. eCollection 2014.

Strength after endurance or endurance after strength training?

All endurance athletes (runners, cyclists, cross-country skiers…) need some strength training. Personally, I prefer to train for endurance and strength on separate days, but for many of us it is more time-effective to combine the two in one session. If that is your case, what do you do first?

© Phil Date | Dreamstime Stock Photos
© Phil Date | Dreamstime Stock Photos

This is an important question, as research has shown that endurance and resistance training lead to different adaptations. Strength training leads to increased muscle mass, while endurance training will allow you to use the available energy and oxygen more effectively and exercise for longer. If you combine both in one session, you will not have any recovery between them and it might be impossible for your body to benefit fully from both. If so, the order in which you do them (first endurance and then strength or the other way around) is important.  Getting it wrong could make a big difference.

Most, if not all, runners I know will start by endurance exercise, and according to Moktar Chtara and his colleagues that is indeed the right thing to do. They divided 48 young men in five groups. The first group performed endurance training only, the second strength training only, the third endurance plus strength and the fourth strength plus endurance workouts. The fifth group did not train and served as a control group. After 12 weeks the endurance plus strength group outperformed every other group during a 4 km run time trial, and their VO2max had improved most.

In the September issue of Medicine & Science in Sports and Medicine however, Moritz Schumann and colleagues published a study suggesting that this does not matter for cyclists. They divided 34 young men in two groups, one of which performed endurance plus strength workouts and the other strength plus endurance. The endurance part of the sessions consisted of cycling, and the strength part of exercises for all the major muscle groups but mainly for the legs.

Both groups improved in strength, VO2max and time to exhaustion, but after 24 weeks there were no significant differences between the groups. The researchers concluded that as endurance cycling is biomechanically similar to many of the strength exercises, they could enhance each other’s effect. Running is of course different.

Surprisingly, Schumann could not notice any significant reduction in body or visceral fat, or in cholesterol levels. Studies whereby the participants perform strength and endurance workouts on separate days on the other hand, typically do show improvements.  The researchers could not really explain this discrepancy: did the participants not train frequently enough (as they did two sessions worth in one go)? Only further studies can figure this out…

In the meanwhile, I’m going to continue planning my endurance and strength workouts in separate days.

References

M Chtara. K Chamari, M Chaouachi et al.  Effects of intra-session concurrent endurance and strength training sequence on aerobic performance and capacity. Br J Sports Med. 2005; 39:555-560.

GA Nader. Concurrent strength and endurance training: from molecules to man. Med Sci Sports Exerc. 2006; 38(11):1965-1970.

 M Schumann, M Kuusmaa, RU Newton et al.  Fitness and lean mass increases during combined training independent of loading order. Med Sci Sports Exerc. 2014; 46(9): 1758-1768.

Sleep enough to keep slim

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© Peter Elvidge | Dreamstime Stock Photos

 More and more people are overweight or obese and at the same time more and more people do not sleep enough. Could there be a link? Scientists have studied this problem by asking participants to reduce their sleep, usually from 8.5h/day to 5.5 h/day. They then noted what and how much the participants ate, and measured any hormone or body weight changes. Most of them would now answer yes indeed, there is a link.

It is clear that nobody believes that you can sleep excess weight off, but not sleeping enough (less than 7 hours/day) can hamper your efforts to slim down or keep your weight under control.

At a first glance this looks unbelievable, as when you are awake for longer, you are going to spend more energy.

The energy you spend consists of 3 components:

1) what you need to keep your body going (your basic metabolic rate),

2) the amount needed to assimilate food,

3) the energy used for all kinds of exercise and activities.

When asleep, you will not eat or move and your basic metabolic rate is reduced by 20-30%. Scientists have calculated that sleeping 5.3h instead of 8h would increase the amount of energy you spend by 45 kcal/d.

However, it is here that your unconscious brain starts interfering. As we have seen in some previous posts (e.g. here or here), your brain wants to keep you safe and it therefore wants your energy balance to remain the same. The balance between the energy you take in and the energy you spend determines your body weight, and depends on genetic, psychological and behavioural factors. Even if it sets your body weight a bit too high for your health, your brain will be unwilling to change it, as anybody who has ever tried to lose weight knows only too well.

Experiments have shown that when you have not slept enough, your brain will stimulate you to eat more to compensate for the energy you have spent. Unfortunately, it will make you overdo it. It will do so by making food more rewarding, and the data show that you will tend to snack more and to choose more fatty and carbohydrate-rich food. This is easily done in our modern world where food is widely available.

© Remigiusz Oprzadek | Dreamstime Stock Photos
© Remigiusz Oprzadek | Dreamstime Stock Photos

It is easy to see how all this will put your best efforts to stay slim in jeopardy. Moreover, a study by Arlet Nedeltcheva showed that dieters who slept for only 5.5 h/day lost more lean body mass and less fat than dieters who slept for 8.5h. They also suffered more from hunger.

Researchers have also studied the effect of insufficient sleep on next day’s activities. Even though some of them have not observed any effect, most report more sedentary time and less vigorous workouts. The discrepancy might be due to the fact that some study participants were used to insufficient sleep, or to the short duration of some studies which could not capture the full effect on people who exercise a few times a week.

There are still plenty of questions to be answered, e.g. what is the effect of habit, is there a difference between men and women, is what scientists observe in a study the same as what happens in real life etc…We do not know either what the effect of physical exercise is: regular exercise improves your sleep, which would then influence your energy balance. Nevertheless, it is a good idea to make sure you have enough sleep!

 

References

JP Chaput and MP St-Onge. Increased food intake by insufficient sleep in humans: are we jumping the gun on the hormonal explanation? Front Endocrinol (Lausanne). 2014; Jul 15;5:116. doi: 10.3389/fendo.2014.00116. eCollection 2014 (accessed 26/08/2014).

A V Nedeltcheva, J M Kilkus J Imperial et al. Insufficient sleep undermines dietary efforts to reduce adiposity. Ann Intern Med. 2010; 153(7): 435-441.

P D Penev. Update on energy homeostasis and insufficient sleep. J Clin Endocrinol. Metab. 2012; 97(6): 1792-1801.

MP St-Onge. The role of sleep duration in the regulation of energy balance: effects on energy intakes and expenditure. J Clin Sleep Med. 2013; 9(1): 73-80.

Do we snack because we are bored?

Several studies have shown that television watching makes you snack more, which is very dangerous for your waistline, while others have found no effect. Could this discrepancy be due to the content of the programmes? If so, choosing your programs wisely would help you to keep your weight under control.

© Kmitu | Dreamstime Stock Photos
© Kmitu | Dreamstime Stock Photos

It is possible that your mood, in particular your level of boredom, could influence how much you are eating. To check this out, Colin Chapman and his colleagues compared how much 18 normal-weight women snacked when watching an engaging comedy program, with what they ate looking at a boring lecture or reading a boring text. The snacks consisted of grapes and M&M chocolates.

The women snacked significantly less during the engaging television program than during the boring one or while reading the boring text. There was no real difference between the amount snacked while reading or watching something boring.

Previous studies have already shown that obese people tend to eat more when bored, but now more and more researchers think that everybody does so. Moreover, if Colin Chapman is right it would mean that being bored by other means than television watching (in this experiment: reading) is just as bad.

The researchers also noted that when bored the women snacked more on grapes than on chocolates. When captivated however, they had relatively more chocolate. They suppose that when the women had more time to choose, they went for the healthy option. Even so, they took in more calories than when they were captivated.

Of course, this experiment was conducted in a lab and the women might behave otherwise when at home. The researchers did not check what the women ate after the experiment and we therefore do not know if there was any effect on the size of their meal.

We do not know either what the women were used to do. Habits are powerful, and if you are used to snack while watching television or if you associate snacking with having a good time, you will find it harder to control it.

Even so, if you want to keep your snacking under control, you should avoid boring stuff… Alternatively, you could make sure that there are no snacks available when you have boring things to do, which is probably a more realistic solution.

References

CD Chapman, VC Nilsson, HA Thune et al. Watching TV and food intake: the role of content. PLoSOne. 2014; 9(7): e100602. doi: 10.1371/journal.pone.0100602. eCollection 2014.

A cold drink to exercise in the heat?

Could consuming cold drinks or ice slush during workouts in the heat help you to perform better? Scientists have been wondering this for many years.

Theoretically it makes sense: as your brain’s main objective is to keep you safe, it will force you to slow down or even stop if it presumes that your core temperature could increase to dangerous levels before the end of the workout. Anything that helps you to keep your core temperature down is thus beneficial, and as cold drinks could act as a heat sink they could be helpful indeed. Scientific studies however, have been inconclusive.

© Dnally | Dreamstime Stock Photos
© Dnally | Dreamstime Stock Photos

Florence Riera and her colleagues have just published the latest study about this problem in PlosOne. They compared the effects of a cold (3 C), ice slush (-1 C) or neutral drink (23 C) with or without menthol flavouring on the performances of 12 trained male cyclists in hot and humid conditions.

The cyclists were randomly assigned a beverage and performed a 20 km time trial in the lab, which means that each of them did the test 6 times (once with each beverage). The performance was better using ice slush whatever the aroma, and better with menthol whatever the temperature. Ice slush or cold water with menthol flavouring was therefore the best.

The researchers concluded that a cold or ice slush drink interferes with the rise in core temperature, allowing you to exercise harder without – or with a smaller- increase in core temperature. 

Menthol usually provokes a sensation of freshness, it is a bit stimulating and it improves the airflow (that is why you use menthol lozenges when you have a cold), but exactly how it works is unknown.

Drinking ice slush is probably possible when you are cycling on a turbo trainer or in the gym, but what can you do if you are a road cyclist? You could try to cool down your core in advance, and researchers have shown that ice vests or cool water baths are helpful indeed.

Pre-cooling techniques are usually unavailable for recreational athletes, but cold drinks can easily be obtained before the start of any event. Christopher Byrne and his colleagues therefore wanted to find out if you could pre-cool yourself with cold drinks.

Seven male cyclists ingested 900 ml cold (2 C) or neutral (37 C) water over 35 minutes before cycling as many kilometres as possible for 30 minutes in a lab. When the athletes drank cold water they cycled 2.8% further and their core temperature (as estimated by rectal temperature measurements) was lower at the end of the test. They felt really cold before starting off though, and one of them was even shivering. Most of them needed to urinate before the exercise. Probably not a very pleasant experience….

© Denise Scott Jackson | Dreamstime Stock Photos
© Denise Scott Jackson | Dreamstime Stock Photos

I wonder if this kind of pre-cooling is possible for runners, as such a large amount of fluid is likely to create gastro-intestinal discomfort? I guess that the only thing runners can do is to get acclimatised and to accept that we will be slower…Or do you have a better idea?

References

C Byrne, C Owen, A Cosnefroy et al. Self-paced exercise performance in the heat after pre-exercise cold-fluid ingestion. J Athl Train. 2011; 46(6): 592-599.

 F Riera, TT Trong, S Sinnapath et al. Physical and perceptual cooling with beverages to increase cycle performance in a tropical climate. PLoSONE 9(8): e103718. doi:10.1371/journal.pone. 0103718. (Accessed 09/08/2014).

R Tucker. The anticipatory regulation of performance: the physiological basis for pacing strategies and the development of a perception-based model for exercise performance. Br J Sports Med 2009; 43: 392-400.

 Disclaimer: this article is for general information only, and does not replace medical advice. It cannot be used to diagnose or guide treatment. If you have any concerns or questions, you should talk to a qualified health provider.

Talent for sport and risk of cardiovascular disease: is there a link?

Have you ever wondered if fellow runners who beat you at races are less at risk of cardiovascular disease than you because they are fitter? Even though we all train hard, some of us improve faster and become better runners. Are they going to live longer and healthier?

© Andre Maritz | Dreamstime Stock Photos
© Andre Maritz | Dreamstime Stock Photos

Both physical activity and fitness reduce your risk of cardiovascular disease, but they are not the same. Physical activity consists of all the voluntary movements that use energy and is therefore a behaviour, while physical fitness is a state of health and athletic abilities. Physical fitness includes aerobic fitness, allowing you to bring oxygenated blood and nutrients to the working muscles, and muscular strength.

Plenty of physical activity improves your fitness, but fitness is also determined by factors such as your age, sex and genetic profile. There is more and more evidence indeed that your genetic profile influences your trainability (the way you respond to exercise), and therefore the athletic abilities and physical fitness you can achieve. The question therefore becomes: if you have an unfavourable genetic profile and do not improve very much even though you are training hard, are you at an increased risk?

I have found only one study about this, and it suggests that as long as we train at the same intensity it does not make any difference. (If you have found more studies, please let me know.)

In 2013, Andrea Chomistec and her colleagues published their results after following 23,016 women for about 14.4 years. The women were part of the Women’s Genome Health Study, and had therefore given a blood sample for DNA analysis when entering the study. They then reported life style characteristics and medical history via questionnaires on a regular basis.

Based on the scientific literature, the researchers selected genetic variants likely to determine fitness, and scored these variants according to the degree they would improve fitness. Andrea Chomistec and her colleagues then compared the scores with the volume and intensity of physical activity and the medical history of the women. As always in studies about genetics, the statistics are complex. As you can now read the article for free, you can check them out for yourself.

Sure enough, the results showed that physical activity reduces the risk of cardiovascular disease, but this was independent of the genetic scores. An unfavourable genetic profile might therefore make it difficult for you to become an elite athlete, but training will reduce your risk just like everybody else’s. This is very good news indeed, because it would mean that reaching your maximal personal fitness matters more than your inborn talent.

© Kmitu | Dreamstime Stock Photos
© Kmitu | Dreamstime Stock Photos

Of course, there are a few problems with this study. First of all, it relies on questionnaires, and the researchers did not have any objective measurements of fitness, such as VO2max. People might over-or underestimate what they are doing, or simply forget, what makes questionnaires not that reliable. Furthermore, it is likely that there are more gene variants that influence trainability and physical fitness than that we know now. This is new science, and this study should be repeated when we have a better understanding if the genetic determinants of fitness. However, it is a large study with a long follow-up, and I think it is the best they could do with the knowledge and funding we have today.

All the participants were women of European ancestry, and we cannot automatically conclude that the results would be the same in other groups. We obviously need more research.

It makes thus sense to increase your physical fitness as much as possible for you, however talented you are. You can do so by training wisely. If you are in doubt how to do so, you should ask a qualified fitness professional for advice.

What should we eat?

If you want to create an animated discussion, start talking about what you should eat (or not) to protect yourself from cancer, cardiovascular disease, diabetes etc… Humans have been wondering which foods to eat since ancient times, but we still have more questions than answers!

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© Skdesign | Dreamstime Stock Photos

Several large studies have shown that we should avoid excess calories, eat plenty of fruit and vegetables, reduce the amount of refined sugars and stay away from processed food, but everything else is still open for discussion. Why is this so?

Nutritional science is based on epidemiological studies, from which researchers try to determine what the effects of different foods or diets are. They can then perform interventional studies, whereby they ask half of the study participants to have more of a specific food or change their diet, and compare the effects with the other half of the participants (= the control group). In the Predimed Study for example, researchers examined the importance of olive oil and nuts in this way. Without good epidemiological studies however, researchers do not know what to look for.

I have just stumbled upon an article by Farin Kamangar and Parisa Karimi explaining how difficult it is to conduct such epidemiological studies, and here comes their list of possible errors and problems.

Measurement errors

The first problem Kamangar and Karimi mention is the way they obtain information about what you are eating. Traditionally this is done via questionnaires and interviews assessing your dietary habits over one year. It is clear that it is difficult to recall accurately what you have eaten over a year. Moreover, you might have changed your diet, and what you have eaten last year is therefore not necessarily reflecting your lifelong habits.

Some researchers ask you to write down what you have eaten for the last 24 hours. Even though you will be able to recall this accurately, it is not sure that you are having something similar each day.

Most questionnaires are really long (80 to 200 items), which can discourage even the most motivated participant.

These problems will hopefully be minimised in the future, as researchers are starting to use online self-assessment questionnaires.

Confounders

Epidemiologists try to find an association between risk factors and diseases. Confounders are factors that independently affect the risk of developing the disease, and therefore falsify the results of the study.

A classical example is the association between coffee drinking and lung cancer. Previous studies suggested this, but as coffee drinkers were more likely to be cigarette smokers, the risk of developing lung cancer had nothing to do with coffee. Another example is the association between lying in bed and dying. As most people die in bed, you would conclude that beds are the most dangerous places on earth.

As confounders are usually unknown, it is easy to see how they can falsify the results. Researchers try to avoid them by comparing populations that are very similar except for the factor they want to study. With this in mind, Beth Taylor and her colleagues compared marathon runners with their non-competitive spouses to examine the effect of strenuous exercise on your arteries.

Variability of food products

Foods are typically grown and/or prepared in different ways in different parts of the world, which might affect their nutritional value. Kamangar and Karimi cite the example of brown rice, which is a healthier choice than white rice since it contains more fibre, but in the United States it has a higher arsenic concentration than white rice. Another example is the difference between grass-fed and grain-fed beef: grass feeding typically results in leaner meat.

The correct control group

As already mentioned above, finding a good control group is a challenge: it has to resemble the study group except for the factor the researchers want to study.

In nutritional science this is very difficult, as the study participants avoiding a specific food usually replace it by something else. For example, imagine what the study results would be if participants abstaining from a specific, probably unhealthy food use to replace it by something containing plenty of simple sugars.

Interactions

Foods contain chemical substances that influence each other’s absorption and actions, and different foods can contain the same substance in different amounts and availabilities. These interactions are very complex, and researchers need large study groups to try to avoid them.

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© John Valenti | Dreamstime Stock Photos

Multiple testing

Epidemiological studies about nutrition are typically large and expensive. Researchers want to use all the data and they therefore test several hypotheses at once. However, there is always a chance to come to a false conclusion by coincidence. Statistically, the probability to obtain such a false positive result is 20%, which means that if you test 20 hypotheses, you will get at least one false positive one.

And therefore…

Nutritional science is fascinating, but difficult. Keep informed, stay critical and be prepared to change your mind.

References:

F Kamangar and P Karimi. The state of nutritional epidemiology: why we are still unsure of what we should eat? Arch Iran Med. 2013; 16(8):483-486.

BA Taylor, AL Zaleski, JA Capizzi et al. Influence of chronic exercise on carotid atherosclerosis in marathon runners. BMJ Open. 2014; 4(2): e004498. doi: 10.1136/bmjopen-2013-004498.

ME Van Elswijck and SH McNeill. Impact of grass/forage feeding versus grain finishing on beef nutrients and sensory quality: the US experience. Meat Sci. 2014; 96(1):535-40.