Does Lack of Protein In Your Diet Drive Weight Gain?

One of the many competing beliefs about how our diet may affect our weight is the “protein leverage hypothesis”.

Simply stated, the notion is that given the importance of protein for the maintenance and functioning of virtually every organ system in our body, we are driven to continue eating till we meet our protein needs – if that means eating extra calories – so be it.

According to this hypothesis, much of obesity related to processed foods has to do with their relative low protein content, which forces us to eat more them in order to maintain the right level of protein intake.

Now a direct test of this hypothesis by Eveline Martens from Maastrecht University, published in the American Journal of Nutriotion, fails to find evidence to support this idea.

This randomized cross-over 12-day study examined the effect of three different diets (5%, 15% or 30% of energy from beef protein) on ad libitum energy intake, body weight changes, appetite profile, and nitrogen balance in around 60 individuals randomized in crossover fashion.

Energy intake was significantly lower in the 30En%-protein condition compared to the 5en% and 15en% condition.

In line with this, hungerand desire to eat ratings were higher and fullness ratings were lower in the 5En%-protein condition than in the 15En%-protein and 30En%-protein conditions.

Although Nitrogen balance was positive in the 15En%- and 30En%-protein conditions, the subjects managed to maintain protein balance on the 5en% diet.

Thus, the study showed that higher levels of protein intake reduce ad libidum energy in take (at least in the short term) whereas restricting protein intake may not necessarily lead to an increase in caloric consumption.

Obviously, enthusiastic supporters of the protein leverage hypothesis will hurry to point out (as do the authors), that the subjects managed to stay in nitrogen balance on the low-protein diet and therefore did not have to increase their energy intake to meet protein demands – this may be different in a longer-term study where eventually lack of protein intake may well influence eating behaviour.

So what this means for obesity management I have no clue. We already know that higher protein diets may be easier to follow and lead to a lower ad libitum calorie intake that low-fat or low-carb diets (at least for some people).

Will cutting your protein intake make you eat more? I’m still waiting for hard evidence on this.

@DrSharma
Edmonton, AB

Martens EA, Tan SY, Dunlop MV, Mattes RD, & Westerterp-Plantenga MS (2014). Protein leverage effects of beef protein on energy intake in humans. The American journal of clinical nutrition PMID: 24760974

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