High-Protein Intake and its Effect on Kidney Function

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A high-protein intake during calorie reduction has been associated with greater weight loss and satiety, and less muscle loss. In athletes or strength training individuals, a high-protein intake has been linked with more muscle mass production, so called muscle hypertrophy. High-protein diets can therefore be favourable when aiming for losing weight or building muscle mass. Read more about this here. However, there are controversies whether a high-protein intake may have negative effects on kidney function. This article provides an update on the latest research on the impact of high-protein diets on kidney function in healthy people.

Recommended Protein Intake

The Nordic Nutrition Recommendations establish that for healthy adults, an optimal protein intake in a varied Nordic diet corresponds to 10-20 % of the total calorie intake. In elderly, the recommended range of protein intake is slightly higher – 15-20 % of the total calorie intake. The World Health Organization and the European Food Safety Authority (EFSA) present a population reference intake of 0.83 g protein per kg body weight and day, both in adults and elderly. Due to the lower energy requirements of elderly people, the recommended protein intake corresponds to a higher percentage of the total calorie intake than in adults, although the recommended grams of protein per kg of body weight is the same in adults and elderly. Similarly, the US recommendation for protein intake is 0.8 g per body weight and day for healthy adults of all ages. The recommendation includes a range of 10-35 % protein of the total calorie consumption. For endurance and strength athletes, the Swedish Olympic Committee recommends a protein intake of 1.2-2.0 g per kg body weight, depending on what type of sport is practiced.

EFSA states that there are insufficient data to establish a tolerable upper level for protein intake. They conclude that intakes up to twice the population reference intake, corresponding to 1.66 g per kg body weight and day, are regularly consumed by healthy adults in Europe and considered safe. For protein intakes above 1.66 g per kg body weight daily, there are currently not enough research to draw conclusions. These numbers refer to healthy adults who are not trying to lose weight. 

As a comparison, imagine that you try to lose weight and follow a high-protein diet of 1600 kcal per day, where 30 % of the calories come from protein. In that case, your protein intake corresponds to 2 g protein per kg body weight if your body weight is 60 kg, or 1.5 g if your body weight is 80 kg. During a high-protein meal plan, the amount of protein intake in grams may be the same as before following the meal plan. However, a reduced carbohydrate or fat intake results in a higher ratio of protein intake relative to total calories consumed.

Kidney Function and Protein Intake

The kidneys control, and are impacted by, the amount of water, minerals and other nutrients in the body. They filtrate our blood to detect waste, regulate the amount of body fluids and balance the release of vitamins, minerals and hormones that we need to stay alive. 

When we eat protein, it is broken down into its building blocks, called amino acids. Subsequently, the amino acids are decomposed, and ammonium ions are formed. Some ammonium ions are required to produce compounds that we need, but to prevent toxic levels of ammonium, a substance called urea is produced from the excessive amounts of ammonium. The urea is removed from the blood by the kidneys through urine, but if the kidney function is reduced, urea will be filtrated at a decreased rate and the urea level in blood rises. A rise of urea levels in blood and urine is also seen after eating protein, since urea comes from the degradation of amino acids. Therefore, a high protein intake in people with kidney damage contributes to a worsened kidney function. 

Additionally, protein intake appears to result in an immediate and more long-term increase of kidney blood flow and filtration rate. These responses are seen in the progression of kidney disease, which is the underlying reason of why a high-protein intake has a bad reputation in relation to kidney health. However, it is not clear if these responses may lead to impaired kidney function in people with healthy kidneys.

Current Research on High-Protein Intake and Kidney Function

Short-term studies on healthy humans have shown contradictory kidney effects of high-protein diets. One of the larger studies in this field, a study by Juraschek et al., compared a high-protein diet (25 % protein of the calorie intake) with a normal-protein diet (15 % proteins of the calorie intake) for six weeks in 164 middle-aged women with prehypertension. They found a significant increase in filtration rate in the high-protein group but concluded that it is uncertain whether a long-term high-protein diet leads to kidney disease. Frank et al. compared a high-protein diet (2.4 g per kg body weight and day) with a normal-protein diet (1.2 g per kg body weight and day) for seven days per diet in twenty-four healthy young men. A significant increase in filtration rate was found due to the high-protein diet.

A long-term study on 1144 middle-aged men and women was conducted by Cirillo et al., where protein intake and kidney function were assessed at baseline and after 12 years. A high-protein intake was significantly associated with higher filtration rate, but a decline in filtration over time, suggesting a lower kidney function. However, Cirillo et al. used a measure of kidney filtration that has several limitations. The effect of protein intake on kidney function was also investigated by Knight et al. in another long-term study over an 11-year period, on 1135 middle-aged women. There was no significant association between protein intake and reduced kidney function in healthy women.

When we get older, our kidneys’ filtration rate naturally declines, which makes it difficult to determine whether reductions in kidney function, seen in studies on middle-aged and older adults with a high-protein intake, is a result of age or protein intake. However, it should be emphasized that a protein intake over 35 % of the total calorie intake should be cautioned.

Summary

When aiming for weight loss, high-protein diets, usually referring to 20-35 % protein of the total energy intake, have been associated with greater weight loss and less muscle loss. There is insufficient evidence for setting an upper limit of protein intake, but EFSA recommends a protein intake of 10-35 % of the calories. However, people with kidney damage should always follow the protein intake recommended from their health care. Lastly, protein intake plays an important role in several processes in the body, involving metabolism, satiety and signalling. These effects of protein seem most apparent when the protein intake is in the higher range of the recommended amounts. Thus, high-protein diets may be beneficial for healthy people in some situations, for example when aiming for weight loss. However, it is important to remember that a protein intake over 35 % of the calorie intake has no additional benefits and an intake of red and processed meat should preferably not exceed 500 g per week. For the sake of your health, always aim for varied, well-balanced and high-quality meals.

Written by Ellinor Nilsson

Further Reading

Cirillo M, Lombardi C, Chiricone D, De Santo NG, Zanchetti A, Bilancio G. Protein intake and kidney function in the middle-age population: contrast between cross-sectional and longitudinal data. Nephrol Dial Transplant. 2014 Sep;29(9):1733-40.

Cuenca-Sánchez M, Navas-Carrillo D, Orenes-Piñero E. Controversies surrounding high-protein diet intake: satiating effect and kidney and bone health. Adv Nutr. 2015 May 15;6(3):260-6. 

Frank H, Graf J, Amann-Gassner U, Bratke R, Daniel H, et al. 2009. Effect of short-term high-protein compared with normal-protein diets on renal hemodynamics and associated variables in healthy young men. Am J Clin. Nutr. 90:1509-16

Juraschek SP, Appel LJ, Anderson CA, Miller ER 3rd. Effect of a high-protein diet on kidney function in healthy adults: results from the OmniHeart trial. Am J Kidney Dis. 2013 Apr;61(4):547-54.

Kamper AL, Strandgaard S. Long-Term Effects of High-Protein Diets on Renal Function. Annu Rev Nutr. 2017 Aug 21;37:347-69.

Knight EL, Stampfer MJ, Hankinson SE, Spiegelman D, Curhan GC. 2003. The impact of protein intake on renal function decline in women with normal renal function or mild renal insufficiency. Ann Int Med. 138:460-7.

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