How High-Protein Diets Slow Metabolism

After learning about how sugar feeds cancer growth, I decided to severely cut back on sugar last year. I initially replaced my morning oatmeal with a protein shake which typically contained a high percentage of protein and low fat. I would also restrict sugar the rest of the day and typically end the day with some keto ice cream.

I noticed several effects from this diet:

1. I felt mentally energized
2. My focus and mental clarity were improved
3. My body fat percentage decreased
4. While I was increasing my muscle mass, my strength seemed to decrease due to lack of energy
5. I began experiencing ammonia in my sweat when working out
6. I had low blood sugar, which resulted in cold clammy hands

I felt better in general and had fewer headaches but I specifically had problems with indigestion. It wasn’t that I had too much acid or heartburn but not enough acid to digest all the protein in my diet.

Studies show that high protein diets increase the production of the hormone glucagon-like peptide-1 (GLP-1), which is has many effects on digestion including regulating gut motility. This effectively increases satiety, but does so by also slowing down metabolism. GPL-1 “inhibits glucagon secretion in a glucose-dependent manner, thus diminishing postprandial glucose excursions.”

Another study showed the GPL-1 “increased [gastric] half-emptying time from 76.6 ± 7.6 min [in controls] to 329.4 ± 71.6 (P < 0.01)”.

Several health websites claim that protein “speeds up metabolism” by taking more energy to digest, but the truth is that protein slows down metabolism and motility.

There are certainly benefits to a high-protein, zero-sugar diet, but there are also drawbacks.

In Zero to Paleo, I describe the concept of appropriating one’s diet. This consists in eating different marconutrients (fat, carbs, and protein) at different times of the day in order to optimize digestion and overall health. The science on GPL-1 bolsters this argument by showing how carbs are important especially early in the day to jumpstart the digestive system and increase motility.