5 little-known facts about protein
Can you survive if you eat only protein?
Can you survive without eating protein?
How does your body keep functioning when you fast?
Do high-protein diets actually promote weight loss, or do they only help you retain muscle when you eat below maintenance?
Our evidence-based analysis on 5 little-known facts about protein features 51 unique references to scientific papers.
Written by Alex Leaf Published: May 21, 2019 Last Updated: Jun 6, 2019
You know protein is important. You know that your protein requirements depend on your health goals, and that protein can minimize fat gains during the holidays and help with dieting in general.
But here are five interesting facts you still might not know.
1. Thermic effect of food
The thermic effect of food (TEF), also known as dietary induced thermogenesis (DIT) and specific dynamic action (SDA), represents the energy (the calories) you need to spend to process what you eat. The TEF consists of two separate components: obligatory and regulatory. The obligatory component represents the energy required to digest, absorb, and metabolize the food. The regulatory component represents the energy lost as heat.
In other words, your body needs to use energy to extract energy from the food you eat. The TEF represents about 10% of the caloric intake of healthy adults eating a standard mixed diet, but your actual number will depend on several factors, which include your lean body mass and the size and composition of your meal.
The bigger your meal and the more lean mass you carry, the longer you’ll keep spending energy to process the food, which is why the TEF should be measured for at least five hours after the meal was eaten.
And the composition of the meal matters because the different macronutrients have different TEFs:
Although it represents but a small percentage of your daily caloric expenditure, the TEF can still amount to several hundred kilocalories each day and so could affect your body composition over the long term. Now you might think, judging from the numbers above, that increasing your protein intake should help you diet down. And well, yes, it should, but probably not because of the resulting increase in TEF — not directly, at least.
One analysis reported that, while protein was the only significant determinant of the total TEF, every 1% increase in calories from protein was associated with a mere 0.22% increase in the total TEF.
Based on these findings, if you were to double your protein intake from 15% to 30%, your daily TEF would increase by only 3.3%. So for each 2,000 kcal you consume (a number that might represent your total daily needs), you’d be spending an additional 66 kcal — a number easily offset by one small apple or a handful of potato chips.
Your body burns more energy digesting protein than it does either carbohydrate or fat, yet increasing your protein intake has a negligible effect on your energy expenditure.However, while increasing your daily TEF by consuming more protein isn’t likely to have a direct effect on weight loss, as we saw, increasing the TEF of a meal might promote weight loss indirectly by increasing satiety, as we’ll see.
Satiety and satiation are often used interchangeably to mean “satisfying hunger”. Technically speaking, however, satiation describes the lack of desire to continue eating a meal, whereas satiety is the feeling of fullness that allows us to stop eating for a while. In this article, when we use the adjective satiating, as in the paragraph below, we refer to satiety.
Protein is the most satiating macro, especially for women, which helps explain why high-protein diets promote weight loss and weight-loss maintenance. But why is protein especially satiating?Although many hormones play a role in regulating appetite, three intestinal hormones have received special attention: cholecystokinin (CCK), glucagon-like peptide-1 (GLP-1), and peptide YY (PYY). Yet none of the three seems a good predictor of the effect that eating more or less protein will have on total food intake, as evidenced by a meta‐analysis of nine studies involving a total of 117 healthy, normal-weight men.
Rather, other factors — such as protein’s high TEF — may explain the satiating effect of high-protein diets. In lean women, greater 24-hour TEF was shown to correlate with greater satiety.
One meta-analysis of individual-participant data from five randomized meal-test studies reported no significant association between satiety and protein intake, but only 8 of the total 111 participants had received meals in which >20% of calories came from protein, whereas protein seems to increase satiety only when it makes for 25–81% of a meal’s calories. Therefore, the lack of an association between satiety and protein intake reported in…