Protein for Satiety: More Isn't Always Better
You've likely heard that protein is more satiating than carbs or fats. While this is often true, the context matters, especially for strength-trained individuals already consuming adequate protein for muscle growth. The question isn't just "does protein make you feel full?" but "does more protein make you feel fuller once you're already meeting your muscle-building needs?"
Our Study: High Protein vs. Even Higher Protein
To investigate this, we conducted a randomized crossover study with strength-trained individuals. Participants followed a diet with a 20% energy deficit for a week, once consuming 1.8 grams of protein per kilogram (0.8 g/lb) of body weight per day (generally sufficient for muscle growth) and another time with a significantly higher intake of 2.9 g/kg (1.3 g/lb) per day.
Our findings were clear: there were no significant differences between the two protein intakes in any measure of hunger (including fullness, desire to eat, and cravings), energy levels, mood, training enjoyment, or training motivation. We also observed no habituation effects, suggesting similar long-term outcomes.
Understanding Protein Leverage Theory
So, why do some studies show protein reducing hunger at higher intakes? This can be explained by protein leverage theory. This theory proposes that our bodies have an innate "protein thermostat" that drives us to consume food until we've met a certain protein threshold. It's similar to our drives for sodium or water; we have mechanisms that ensure we get enough of these essential nutrients.
The theory suggests that when our body has consumed enough protein to fuel anabolism (muscle building), appetite-suppressing responses are stimulated. Essentially, once protein is being efficiently used for muscle protein synthesis, the need for more protein decreases, and so does our appetite. However, once protein intake goes beyond this anabolic threshold and starts being oxidized for energy, there's no further impact on appetite. This evolutionary mechanism makes sense, as our bodies don't efficiently store excess protein like they do fats and carbohydrates.
What the Data Says
A meta-analysis of 38 studies strongly supports protein leverage. It found that up to a protein intake of approximately 20% of total energy intake, there was indeed a decrease in overall energy intake when people were allowed to eat freely. However, at protein intakes higher than this, there was no significant further decrease in energy intake. This breakpoint of ~20% of energy intake corresponds to about 1.2 g/kg (0.5 g/lb) per day, which aligns with the optimal protein intake for general health and body composition in non-strength training individuals.
Combined with our study, this suggests that for both sedentary and strength-trained individuals, the protein intake required for maximum satiety closely matches the protein intake needed for optimal body recomposition.
Conclusion: Focus Beyond Just Protein for Satiety
If you're already consuming enough protein for optimal body recomposition (around 1.8 g/kg or 0.8 g/lb per day), increasing your protein intake further specifically for satiety during a cutting phase is often unnecessary.
Instead, when you've met your protein needs for muscle preservation, you're better off focusing on other dietary strategies to manage hunger. Foods rich in fiber and with a low energy density (meaning lots of volume for fewer calories) are often excellent choices for reducing appetite, regardless of their protein content. Examples include fibrous vegetables. While some high-protein foods like egg whites can be very satiating, others, like a whey shake, may not be as effective for hunger control.