High-protein diets are very popular, as they help you to lose weight and increase muscle mass. Unfortunately, they can also lead to chronic metabolic acidosis and harm your health, unless you eat plenty of fruit and vegetables.
The classical recommendation is to get 45 to 65% of your calories from carbohydrates, 20 to 35% from fat and 10 to 35% from protein. High-protein diets (16 to 45% of your calories as protein) are very popular with slimmers as they make you lose weight much quicker than traditional diets. Athletes, even recreational ones such as you and I, are tempted to eat more protein to build up their muscular strength. On the other hand, a diet rich in animal protein can result in metabolic acidosis, which is bad for your health.
In the April 2013 issue of Nutrition Journal, Lukas Schwingshackl and Georg Hoffmann reviewed the studies comparing low-protein with high-protein diets after a 12 month follow-up. They did not find any significant differences in waist circumference, fat mass, serum lipids (e.g. cholesterol), blood pressure or insulin levels. They concluded that as high-protein diets did not offer any advantages and could be dangerous, there are no reasons to adopt them.
Dr Santesso and colleagues had performed a similar review in 2012. They noticed some small improvements in triglycerides levels, blood pressure and waist circumference, but they wondered if these effects were worthwhile compared to the risks.
This brings us to the crucial question: what are these risks? They are linked to the acid-base balance in your body.
Your body keeps your acid-base balance under tight control, and your blood plasma pH is therefore stable. Unfortunately, a diet containing a large amount of animal protein is highly acidic. If the amount of acids increases, your body will buffer it with bicarbonate and your kidneys will excrete more acid. Your will bring your pH back to normal, but your bicarbonate levels will be lower and your urine more acid. This new balance is called metabolic acidosis.
However, as everything is linked and works via chain reactions, a new balance is never good news. It does not have any health implications if it happens only occasionally, but if it continues for many years it can lead to chronic disease.
Even though your kidneys have to work hard to keep your acid-base balance right, high-protein diets do not lead to chronic kidney disease. They will aggravate an existing one though, and you should therefore have a chat with your doctor before embarking on such a diet.
Consequences of a lifelong metabolic acidosis
Metabolic acidosis leads to insulin resistance (= when your cells are less responsive to insulin stimulation) and high blood pressure, and puts you therefore at risk of diabetes and cardiovascular diseases. The situation gets worse as you get older, probably because the kidneys become less able to correct the acid-base balance due to aging.
Recently, scientists have discovered that metabolic acidosis stimulates the formation of reactive oxygen species, which can damage cells and lead to cancer.
Calcium and bones
People who have a high-protein diet lose more calcium via the urine. It is not clear yet why, and it is unlikely to be linked to metabolic acidosis. On the other hand, protein stimulates calcium absorption from the intestine, and therefore scientists have wondered for many years how a high-protein diet affects your skeletal health. Most of them now feel that it is beneficial, but the effect is probably not large enough to make a difference in your fracture risk. As yet, they have not been able to show that plant proteins are better than animal ones.
Advantages of a high-protein diet
A high-protein meal makes you quickly feel full and less hungry at the following meal. As a result you will eat less and lose weight.
The energy you need for the digestion, absorption and disposal of food is called the thermic effect. It seems to be larger for protein than for carbohydrates and fat. Scientists agree that the differences are quit small, but taken over a period of time they become significant.
An adequate protein supply is essential to maintain or increase your muscle mass. Studies have shown that the combination of ingesting protein and resistance training results in the greatest muscle gain. This is not only important for athletes, but also for elderly people, who need to increase -or at least maintain- their strength to remain independent and avoid falls.
Animal or plant products?
Studies have shown that proteins from plants are often less acidic than those from animal products. Moreover, fruit and vegetables contain alkalising substances, such as potassium and magnesium, which will help buffering the acids.
Click here for lists of fruit and vegetables containing proteins.
What does it mean for me?
You could replace part of your refined carbohydrates by proteins from a source poor in saturated fat, as long as you keep your acid-base balance under control by eating plenty of fruit and vegetables. Consult your doctor first.
Disclaimer: this article is for general information only, and does not replace medical advice. It cannot be used to diagnose or guide treatment, or to revise your diet without supervision from a qualified health provider. If you have any concerns or questions, you should talk to your doctor.