In the last post on protein intake, I discussed protein requirements for optimal health and how some of the media buzz encouraging high protein intake may not be required. In this post, I will follow-up on that and also discuss the implications of high-protein diets for health, specifically weight loss.
As one may see, whey isolate (found in whey protein powder) is absorbed at the fastest rate, about 8-10 grams/hour. However, this fast protein absorption is not strongly correlated with a “maximal protein balance” as many fitness experts express (as they slug down a smoothie with scoops of whey protein powder). In my opinion, you’re better off consuming the protein in real food form, such as greek yogurt or a piece of salmon.
Amino acid breakdown occurs in the liver through the urea cycle. The maximal rate of urea excretion, the byproduct created when amino acids are broken down, is quite high. For example, an 80 kg person could technically consume 285 to 365 grams of protein per day without adverse effects such as hyperammonemia and hyperaminoacidemia. However, it’s important to note that protein still contains calories (4 calories per gram) and any excess protein consumed in the body is converted and stored as fat.
On the other hand, a diet that contains adequate levels of protein (g/kg) and even a bit higher than the 0.8g/kg recommendation has advantages. If one continues to consume the same amount of calories, this higher level of protein intake displaces other calories from carbohydrates and fat. Protein increases satiety, the feeling of fullness, and helps in weight control because it has a higher rate of thermogenesis than fat and carbohydrates. Thermogenesis is the production of energy (calories) and occurs faster in protein than other macronutrients, meaning it is less likely to be stored in the body as fat.
Since protein has a greater thermic effect than fat and carbs and greater satiety, there is much evidence that increased protein intake is an effective weight loss strategy. In one study, obese individuals were randomized to either a high-carb diet (fat 30%, protein 12%, Carb 58%) or a high-protein diet (fat 30%, protein 25%, carb 45%). The individuals were allowed to eat ad libitum (no restriction on calories) and followed the diet for six months. After 6 months, individuals in the high-protein group had higher greater weight loss as well as reported satiation from the ability to choose from more protein-rich foods than the other group as well as still being allowed to include complex-carbs in their diet.
Similarly, in another study, 13 obese hyperinsulemic males were divided into two restricted calorie diets: either a high protein diet (protein 45%, 25% carbs, 30% fat) or high carb diet (protein 12%, 58% carbs, 30% fat) for four weeks. After four weeks, the high-protein group had greater weight loss. Further, REE (resting energy expenditure) decreased more in the high-carb group meaning that the high-protein group was able to burn more calories while resting even though restricting calories. Mean fasting insulin decreases significantly in both diet groups, but only reached the normal range in the high protein group. For these reasons, a high-protein diet may also be a good option for overweight and obese patients who are at risk of or have type 2 diabetes as it seems to help regulate blood sugar better than the high-carb diet.
In another study, exploring a high-carb vs. high-protein diet, both groups lost a significant amount of weight. However, the high-protein diet lost more body fat and less lean body mass (muscle) than the high-carb group. These results have also been expressed in other studies (1, 2, 3).
Although these are only a few examples, I think that there is evidence to conclude that high-protein diets may be the better option for individuals, especially those trying to lose weight, especially for satiety purposes as well as glucose regulation and maintenance of muscle. While the diet doesn't have to look like the Paleo diet, it is important to focus on healthful protein sources as well as healthful fat and carbohydrate sources for maximum health. For those trying to lose weight, I recommend making a large proportion of total calories come from protein. That’s the end of my personal posts. The next 5 posts following will be about my specific project on full-fat vs. low-fat dairy! Stay tuned!