Adequate protein is a must for weight loss

protein leverage
Humans strive to maintain a constant protein intake

The protein leverage hypothesis of obesity asserts that humans and animals closely regulate the amount of protein in their diets, with the average human consumption of protein being around 15% of calories. The idea is that if available foods are low in protein, more food will be eaten until protein requirements are satisfied. If foods are relatively dilute in protein, containing, say, less than 15% protein overall, then more calories need to be consumed to make up for the lack of protein. If higher protein foods are eaten, then less calories are consumed and weight loss or maintenance follows.

It’s not hard to see how eating foods lower in protein could lead to becoming overweight.

Is this really true? Do humans and other animals have a sort of “proteinostat” that monitors their protein ingestion and tells them to eat more or less protein? There’s a lot of evidence that they do.

In non-human primates, for example, protein content of foods dictates daily energy consumption. This also appears to be the case with other animals, such as pigs and rodents.

A trial of the protein leverage hypothesis in humans

What we want to know is whether this effect works in humans. Simpson and Raubenheimer, the two main theorists of the protein leverage hypothesis of obesity, set out to test it in a clinical trial in humans: Testing Protein Leverage in Lean Humans: A Randomised Controlled Experimental Study.

What they did was to take 22 “lean subjects” and feed them food that disguised the protein and other macronutrient composition of their diets, and see what happened in terms of calorie consumption. When the composition of the food was only 10% protein, the subjects consumed 12.4% more calories than when protein composition was 15%. However, raising the protein content to 25% from 15% had no effect on calories consumed.

Verdict: “In our study population a change in the nutritional environment that dilutes dietary protein with carbohydrate and fat promotes overconsumption, enhancing the risk for potential weight gain.”

Protein consumption dropped during the obesity epidemic

As the authors note in their paper, between 1961 and 2000, average protein consumption in the U.S. dropped from 14% to 12.5%, an absolute decrease of nearly 11%, and over the same time period, non-protein calorie consumption increased 14%. Absolute protein consumption remained constant, which provides epidemiological evidence for the protein leverage hypothesis.

What has driven the decreased protein intake and the increased calorie intake? Two things, in my opinion. One is the increased consumption of junk food: chips, soda, pastries, and similar things, all of which have a low protein content. The other is the infamous U.S. government dietary guidelines, which tell everyone without exception to eat a low-fat diet. Since protein is often associated with fat, such as in meat and dairy products, these guidelines led to less meat consumption, with more calories being consumed to compensate for the lack of protein in all the empty, high-carbohydrate foods that the government (and the medical establishment) wanted us to eat.

Ensure adequate protein for weight loss

Here we see another possible reason why low-fat diets have such a dismal record in weight loss. The relative lack of protein contributes to people being hungrier, and you can only defend against hunger so long before you give in.

In contrast, low-carbohydrate diets typically have a higher protein content and by all accounts people are much less hungry when eating low-carb. Usually, calorie intake on a low-carbohydrate diet spontaneously decreases, and increased protein consumption may be one reason why. Higher protein diets produce greater satiety.

It appears that if one wants to lose weight, ensuring a decent level of protein consumption is important, since that means less hunger and a consequently lower calorie intake. This can be done on most low-carb diets, since they usually entail foods that are relatively high in protein. By definition, most low-fat diets are low in protein, and most people are doomed to fail on these diets.

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5 comments
Aaron says May 16, 2015

If absolute protein remained constant, but protein percentage of total diet went down, then that means people weren’t eating less protein but simply eating more non-protein.

So people’s protein consumption did not go down but their non-protein consumption went up. This means their increased non-protein consumption wasn’t driven by a decline in protein consumption but must have another explanation.

So this theory does not add up.

BTW, chips – potatoes – has protein. In fact potatoes are considered a complete meal and one of the healthiest foods you can eat. If you think lots of fat and salt are bad for you you’ll think chips are unhealthy, but if you think high fat is fine and salt isn’t bad, chips are in fact a very healthy food.

Reply
    P. D. Mangan says May 17, 2015

    It means that they ate enough to reach ~15% calories as protein, or enough to maintain absolute protein amount. Theory still stands.

    Reply
Aaron says May 17, 2015

Ok, that makes sense. I guess if you suddenly start eating food with less protein, you’ll eat more to get the same amount of absolute protein. So absolute protein won’t change but calories will go up. If you shifted the kind of food you eat.

But I don’t get the percentage thing, tho. If you’re eating more calories to get the same amount of absolute protein, then the percentage of protein as part of diet would have to go down.

Getting a 15% protein as part of total diet would have more to do with what kind of food you ate and less to do with how much you ate. Bread has protein – if all you ate was bread, you’d never get to a 15% protein as part of diet even if you ate enough bread to fulfill some absolute protein needs. As long as the body is getting its protein needs met on 1% protein as percent of total calories, why should it matter?

So the relevant metric has to some absolute protein needs, not protein as percentage of diet.

What is the actual minimum protein needs of the body, and would a typical American junk food diet fail to meet this minimum need?

I think that has to be the relevant question. Did the switch to high carb diets in the 70s make many people have to eat more food to satisfy their minimum protein needs?

Reply
    P. D. Mangan says May 17, 2015

    You’re right about the percentage, which dropped from 1961 to 2000. It would have to be an absolute amount. The actual minimum protein needs of the human body are, strange to say, unknown. We know that if you got totally minimal amount, you might get kwashiorkor or succumb to infections. And we know that on a lower amount than the RDA, physiology changes, and other changes occur with an amount higher than RDA, some beneficial – higher glutathione – others more mixed, like higher IGF-1. But no one can say that humans must have x amount, as far as I’m aware.

    Reply
      Aaron says May 20, 2015

      Interesting. Thanks for the response, Mangan. More study needs to be done, for sure.

      Reply
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