Is a Protein Deficit Driving Obesity Trends?

Macronutrient explanations for obesity have had a rough ride. Too much fat was supposed to be the culprit. Then the focus turned to refined carbs and sugar. By themselves, those were not especially enlightening tangents for the public. Some people still push back on excessively fatty foods. Sugar still counts as a dietary bad actor. But ketogenic and low-carb diets are losing their hold on people. So is the time right to embrace the thinking that says the real problem is a deficit of protein in our ultra-processed food supply driving obesity trends?

That’s the direction a new featured paper in Obesity is pointing. Amanda Grech and colleagues tell us:

“Highly processed discretionary foods are a significant diluent of protein and associated with increased energy but not increased protein intake.”

And thus, they believe that:

“Low-protein highly processed foods lead to higher energy intake because of the biological response to macronutrient imbalance driven by a dominant appetite for protein. This study supports a central role for protein in the obesity epidemic, with significant implications for global health.”

An Ecological Analysis

Grech et al tested their protein leverage hypothesis using dietary data in an ecological analysis using multi-dimensional nutritional geometry. Yes, that’s a mouthful. But what it means is that they used Australian nutrition survey data to test the idea that human regulation of protein intake leads to increased energy consumption when carbs and fat serve to dilute the protein in the food supply.

The problem, they say, is that ultra-processed foods tend to have less protein than diets of minimally processed and whole foods. So the human appetite for protein drives people to eat more calories than they need in order to get enough protein to satisfy their bodies.

Professor Stephen Simpson, one of the authors of this new paper, tells us that “understanding the mechanism is really important, but I think we know enough already to start that work” on the quality of the food supply. He explained all this on the second day of the recent Royal Society meeting about the causes of obesity. He also made the case that we should be pressing forward to reduce consumption of ultra-processed foods while also reformulating them to address their deficits.

Yes, But…

Let’s remember. This compelling idea, though backed by experimental evidence and ecological analysis, remains a hypothesis. Unintended consequences have a way of cropping up.

For instance, at ObesityWeek, Carol Johnston and Minghan Pang presented data on a double-blind crossover trial of adding high-protein nutrition bars to the diets of healthy, young non-athlete adults. All that extra protein did not lead them to eat fewer calories in the rest of their diets. Instead, it led them to consume more energy and gain fat mass in the weeks when they consumed these bars.

No doubt, protein leverage is a fascinating hypothesis. But thus far, act now and sort out the understanding of obesity later has not led us to good results for public health in obesity. We have our doubts that it will serve us well in the future.

Click here for the new study in Obesity, here for Simpson’s lecture at the Royal Society Meeting, and here for Johnston and Pang’s study from ObesityWeek.

Rib of Beef, painting by Gustave Caillebotte / WikiArt

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November 21, 2022