Protein is an essential macronutrient needed by the human body for growth and maintenance.

Foods rich in animal protein are meat, fish, eggs, poultry, and dairy products, while plant foods high in protein are mainly legumes, nuts, and grains.

With this in mind, what is the current recommended dietary allowance (RDA) for protein for an adult?

1. 0.18 g protein/kg body weight/day.
2. 0.8?g protein/kg body weight/day.
3. 1.5?g protein/kg body weight/day.
4. 1.0?g?protein/kg body weight/day.

Look below for the correct answer and further information

The correct answer is 2.

The current recommended dietary allowance (RDA) for protein is:

• 0.4 g protein/kg body weight/day. Eating less than this can lead to a protein deficiency, which is a very serious condition.
• 0.8 g protein/kg body weight/day for adults. However, this is based on structural requirements and ignores the use of protein for energy metabolism (Bilsborough & Mann, 2006).
• 1.5 g protein/kg body weight/day for children.
• 1.0 g protein/kg body weight/day for adolescents.

The key issues for protein intake are:

1. The rate at which the gastrointestinal tract can absorb amino acids from dietary proteins (1.3 to 10 g/h); and
2. The liver’s capacity to deaminate proteins and produce urea for excretion of excess nitrogen (i.e. high protein diets may exceed the liver’s capacity to convert excess nitrogen to urea).

Research (Bilsborough & Mann, 2006; Delimaris, 2013) suggests there are a number of adverse effects associated with long-term high protein/high meat intake in humans (defined as when protein constitutes >35% of total energy intake), including:

1. Hyperaminoacidemia: Refers to the condition of having an excess of amino acids in the bloodstream. There is evidence that hyperaminoacidemia increases protein synthesis and anabolism.
2. Hyperammonaemia: Is a metabolic disturbance characterised by an excess of ammonia in the blood. It is a dangerous condition that may lead to brain injury and death.
3. Hyperinsulinemia nausea.
4. Diarrhoea.
5. Disorders of bone and calcium homeostasis.
6. Disorders of renal function.
7. Increased cancer risk.
8. Disorders of liver function.
9. Precipitated progression of coronary artery disease.
10. Even death (google “rabbit starvation syndrome”).

Reviews (Bilsborough & Mann, 2006; Delimaris, 2013) suggests that there is currently no reasonable scientific basis in the literature to recommend protein consumption above the current RDA (aka a high protein diet) for healthy adults due to its potential disease risks.

Bilsborough & Mann (2006) argue “A suggested maximum protein intake based on bodily needs, weight control evidence, and avoiding protein toxicity would be approximately of 25% of energy requirements at approximately 2 to 2.5 g x kg(-1) x d(-1), corresponding to 176 g protein per day for an 80 kg individual on a 12,000kJ/d diet. This is well below the theoretical maximum safe intake range for an 80 kg person (285 to 365 g/d).”

References

Bilsborough, S & Mann, N. (2006) A Review of Issues of Dietary Protein Intake in Humans. International Journal of Sport Nutrition and Exercise Metabolism. 16(2), pp.129-152.

Delimaris, I. (2013) Adverse Effects Associated with Protein Intake above the Recommended Dietary Allowance for Adults. ISRN Nutrition. 126929. Published online 2013 Jul 18. doi: 10.5402/2013/126929. [Accessed: 22 Janury, 2018].