The Dangers Of High-Protein Diets

Protein is necessary for the build and repair of muscles, hormone synthesis and energy production. It is a building block for bones, cartilage, muscles and skin, making it a crucial part of a healthy diet. However, is it possible to consume too much protein?

The craze surrounding protein peaked in the 1950s when protein deficiency was identified as a widespread global issue by the United Nations. This was sparked by the discovery of Kwashiorkor, a disease of malnutrition, which was initially assumed to be caused by protein deficiency. It was discovered by Dr Cicely Williams, who then spent the latter part of her career debunking the theory she first identified.

This contributed to estimates of protein needs, which then initiated the production of protein supplements to close the “protein gap”. In 1974, the protein gap was finally exposed as a myth by Donald McLaren, who described it as “one of the greatest errors committed in the name of nutrition science”.

A year after McLaren’s announcement, an analysis of diets of children in developing countries revealed that protein deficiency was rare, and a deficiency was caused by a lack of food rather than the low-protein content of food. Low-protein staples, such as yams and cassava, were found to contain enough protein for human needs. Therefore, the protein gap theory and theory of kwashiorkor as a disease of protein deficiency were quashed. To this day the diagnosis of kwashiorkor is still unclear.

What are the risks of high protein intake?

Multiple high-quality, peer-reviewed studies indicate high protein intake and the overuse of protein supplements cause disorders in human health. Diets high in protein generate large amounts of acid in body fluids, which the skeleton responds to by resorbing bone. Acid loading also directly inhibits calcium reabsorption in the kidneys, leading to bone loss and hypercalciuria (excess urinary calcium secretion). This can lead to impaired kidney function, calcium kidney stones and an increased risk of musculoskeletal disorders.

The formation of kidney stones is increased by 250% with high ingestion of animal protein. In a 12-day study, individuals were fed diets containing either vegetable protein, vegetable and egg protein, or animal protein. It was found that the animal protein diet had the highest excretion of uric acid, leading to an increased risk of stone formation. High protein intake was also associated with accelerated decline in kidney function in women with mild renal insufficiency.

In a cohort study, women who consumed 95 grams of protein per day, compared to 68 grams per day, were found to be at increased risk of forearm fracture. Moreover, women who ate five or more servings of red meat per week were also at increased risk, compared to women who ate one serving or less.

Several studies found a correlation between high protein intake and the development of stomach, colon, rectal, pancreatic, bladder, breast, endometrial and ovarian cancer, irrespective of other dietary factors, physical activity, body weight, alcohol intake, cigarette smoking or aspirin use. Men who consumed animal-based proteins five or more times per week had a significantly increased risk of colorectal cancer, compared to men consuming these foods less than once per month.

High protein intake is also associated with liver dysfunction and coronary artery disease (CAD). In a case-control study, individuals assigned to the high-protein group showed worsening of CAD markers, in comparison to the treatment group, suggesting that high-protein intake increases the progression of cardiovascular disease via increases in inflammation, fat accumulation and coagulation pathways.

In summary, the adverse effects associated with high-protein diets include disorders of bone and calcium balance, kidney dysfunction, increased cancer risk, liver dysfunction and increased risk of cardiovascular disease. Therefore, there is no justifiable reason to increase protein intake above the recommended daily intake.

How much protein should I be having?

The recommended daily intake (RDI) of protein, as determined by the National Health and Medical Research Council of Australia, are good measures to follow. For women aged 19-70, the RDI is 0.75 g per healthy kg of bodyweight and increases to 0.95 g/kg over the age of 70 and for athletes. For men aged 19-70, the RDI is 0.84 g per healthy kg of bodyweight and increases to 1.07 g/kg in the elderly and athletes.

If you’re unsure of how much protein you need, my Custom Meal Plan offers a complete guide to meals you should be eating to reach your health goals, along with detailed nutrient breakdowns, shopping lists and recipes.

References

Delimaris I. (2013). Adverse Effects Associated with Protein Intake above the Recommended Dietary Allowance for Adults. ISRN nutrition, 2013, 126929. https://doi.org/10.5402/2013/126929

Greger, M. (2016). The great protein fiasco. NutritionFacts.org. https://nutritionfacts.org/video/the-great-protein-fiasco/

Ketchell, M. (2017). The protein gap - nutritional science’s biggest error. The Conversation. https://theconversation.com/the-protein-gap-nutritional-sciences-biggest-error-76202 

McLaren, D. S. (1974). The great protein fiasco. The Lancet. 305(7872), 93-96. https://doi.org/10.1016/S0140-6736(74)91649-3

National Health and Medical Research Council. (2014). Protein. https://www.nrv.gov.au/nutrients/protein 

Waterlow, J., & Payne, P. (1975). The protein gap. Nature, 258. 113–117. https://doi.org/10.1038/258113a0