Protein and Fullness: Why High Protein Diets Work

Of the three macronutrients, protein is the one that makes it easiest to eat less. That is most of the reason higher protein diets tend to outperform in weight loss trials, and the reasons are mechanical rather than magical.

Protein and the hunger signals

When protein reaches the small intestine, the gut releases hormones that tell the brain the meal is landing. Two of them, PYY and GLP-1, rise more after a protein rich meal than after the same calories from carbohydrate or fat. At the same time ghrelin, the hormone that drives hunger, drops further and stays down longer. The practical result is a meal that tends to hold you well into the afternoon instead of fading by mid morning.

This shows up in intake. In one well known trial, adults who moved from a standard diet to one with 30 percent of calories from protein, with no instruction to eat less, cut their daily intake by several hundred calories on their own and lost weight over 12 weeks.

There is a second, quieter effect. Digesting protein costs energy. Roughly 20 to 30 percent of the calories in protein are burned processing it, compared with roughly 5 to 10 percent for carbohydrate and almost nothing for fat.

The part that matters most

The strongest case for protein in a weight loss plan is what it protects. In any calorie deficit the body pulls from fat and from muscle. Protein, especially alongside resistance training, shifts that split toward fat. Keeping muscle limits the drop in resting metabolism, keeps the strength that drives the next round of progress, and keeps the body you end up with worth having.

This is also why I diagnose obesity by body fat percentage rather than BMI. Two people can lose the same 30 pounds, and the one who kept the muscle is in a different place.

The target

We set protein at 1 gram per pound of lean body mass per day, not total weight. Lean mass comes from a DEXA or InBody scan, and the number is usually lower than people expect. A 200 pound man at 25 percent body fat has 150 pounds of lean mass, so his target is 150 grams, spread over 3 to 4 meals of 30 to 50 grams each. Spreading it matters because each meal of 30 grams or more gives the muscle a fresh signal to build, and several of those across the day appear to work better than one large dose.

A hypothetical 42 year old woman who has been living on cereal, salads and 60 grams of protein a day often notices she is less hungry within a week or two of bringing it up to her lean mass target, before the scale moves at all.

That's the kind of thing we measure, and the first step is knowing your lean mass.

This article is educational and is not medical advice.

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