Personal trainers and other calorie-counting aficionados will tell you that a "calorie is a calorie" and you need to reduce your total caloric intake below what you burn each day in order to lose weight. Within this general guideline, you'll often hear the mantra "all foods fit:' which tells us that we should follow the Food Guide Pyramid— but we can splurge as long as we count the calories in our Twinkie or candy bar.
Calorie counting does work, to an extent, but it completely ignores the fact that we lose fat, muscle and even a little bone when we lose weight, and the goal should be to maximize fat loss while minimizing muscle loss (some loss in bone density is normal, since we are carrying around less weight overall). And, the calorie balance equation oversimplifies the multitude of factors involved in weight control and ignores one very important variable: hunger.
To eat fewer calories than you burn, you must control both your physiological hunger and all of those psycho-logical aspects that are involved in food intake. If you set out on your weight loss journey by eating fewer calories, what do you do when you get hungry? You could snack on lettuce with calorie-free dressing or chow down on a plate of steamed vegetables to fill up your stomach. Or, you could control your hunger by adding protein or amino acids to your meals and snacks.
There is an ongoing debate among scientists and consumers alike that pits grains against protein. Some swear by a diet rich in low-fat grains for long-term weight loss success, while others stand by protein and snub grains. And those who sit in the middle opt for the Mediterranean diet approach, a nice balance of healthy fat, protein and carbohydrates.
Regardless of what side of the fence you sit on, no one can ignore the research. And the body of research on diets varying in macronutrient (carbohydrate, protein and fat) content tells us that low-carbohydrate diets, unrestricted in total calorie intake, are at least as effective as low-fat, energy-restricted diets for weight loss. Low-carbohydrate diets are especially effective for weight loss in the short term, defined as six months or less.
A few theories have been proposed to explain why low-carbohydrate diets are more effective than low-fat diets in the first several months of dieting.The first theory is that higher-protein, lower-carbohydrate diets increase calorie expenditure. This seems plausible because we know that more calories are burned digesting protein than carbohydrate or fat and that the difference is dramatic, approximately 0-3 percent for fat, 5-10 percent for carbohydrates and 20-30 percent for protein (though this thermic effect of feeding is reduced in obese, insulin-resistant patients).
No significant differences have been noted in after-meal calorie burn (called postprandial thermogenesis) in patients on a low-carbohydrate versus low-fat diet. So let's put that theory on the back burner for now.The second, very believable theory is that low-carbohydrate diets decrease our glycogen stores (carbohydrate is stored in the body as glycogen in the muscle and liver). However, this theory has also been debunked after studies have found that changes in body composition have failed to show a major decrease in fat-free mass (which includes muscle and hence glycogen in the muscle).The third theory, which still holds credence, is that the protein in low-carbohydrate diets increases our feeling of fullness and satisfaction, thereby decreasing our ad lib caloric intake. And, an in-depth look into our body's physiology helps explain the science behind the satiety-inducing effects of protein.
Both human and animal studies show that protein and amino acids are more satiating than carbohydrate and fat in the short-term. By examining hormone release and amino acid levels in the blood, scientists have uncovered how the "what we eat" part of the equation affects feedback loops to the hypothalamus in our brain, the area that regulates appetite, energy expenditure and metabolism.
When protein or amino acids make their way to our stomach and intestines, hormones are released that act on peripheral nerves to control food intake. And, these same hormones (cholecystokinin, glucagon-like peptide 1 and peptideYY, aka CCK, GLP-1 and PYY) are carried in the blood to the brain where they influence the hypothalamus to suppress food intake.
In addition to affecting the release of these satiety-inducing hormones in the gut, amino acids, especially the branched-chain amino acid (BCAA) leucine, may play an especially important role in letting our brain know we are full. BCAAs regulate the circuits in our brain that control appetite and energy balance through a pathway called mTOR. Animal studies show that direct administration of leucine activates mTOR signaling, leading to appetite suppression and weight loss over time. Animal studies also indicate that diets with an excess of leucine may decrease food intake by up-regulating the production of the satiety-inducing hormone leptin in fat cells.
It's clear that protein plays a key role in satiety. But, are certain types of protein better than others? Few comparison studies have examined one type of protein in comparison to others. In fact, no studies have examined a wide spectrum of types of protein and their effect on satiety— protein from red meat, poultry, eggs and milk for instance. However, milk proteins are unique because they contain glycomacropeptide— a chain of amino acids that stimulates that satiety-boosting hormone, CCK.
Whey also contains more BCAAs and leucine in comparison to other types of protein. According to Jose Antonio, Ph.D., FISSN, CEO of the International Society of Sports Nutrition, "The milk-based protein whey may be one of the best sources of protein for inducing satiety." In a study comparing the satiety-boosting effects of whey, casein and soy in healthy young subjects, whey protein decreased hunger to a greater extent as measured by a visual analogue scale. However, whey consumption didn't alter calories consumed at the next meal, in comparison to casein or soy.That study alone may not be terribly convincing, but two additional studies also lend credence to the beneficial effects of whey on satiety. In one of these studies, 48 grams of whey, in comparison to 48 grams of casein, taken 90 minutes prior to a meal, resulted in greater subjective ratings of satiety, decreased food intake at the meal, and a significantly greater increase in the release of two of the satiety hormones— CCK and GLP-1.
Likewise, another study found that consumption of a breakfast custard containing 10 percent whey versus 10 percent soy or casein increased satiety and decreased hunger ratings 180 minutes post-consumption. Whey also triggered the greatest increase in GLP-1.
Adding protein is clearly beneficial and doing so at breakfast, the meal where people typically skimp on protein, may be especially important in helping increase satiety and decrease subsequent caloric intake through the day. In a study in overweight and obese adults, subjects consumed a breakfast of eggs, or the same calorie amount in bagels. Both groups ate lunch 3.5 hours later, yet those who had consumed eggs consumed significantly fewer calories throughout the day, than the group that ate the bagel-based breakfast.
Though low-carbohydrate and very low-carbohydrate diets may not be suitable for everyone, the take-home message is clear. If you want to lose weight, add protein or the branched-chain amino acids to your diet.The three BCAAs, especially leucine, may help you feel full and the BCAAs stimulate protein synthesis and inhibit protein breakdown.
How much protein or BCAAs do you need at each meal and snack to maximize your satiety levels? It's too early to tell, and the amount you need is likely very individual and dependent on your current state of nutrition (weight, body fat, activity level and calories consumed daily). However, you should aim for 20-25 grams of protein per meal (the amount we know helps maximize protein synthesis) and choose snacks that contain protein as well. Some easy choices include low-fat string cheese, egg whites, turkey jerky, protein bars and ready-to-drink shakes (RTDs).
Written by Mario Spano, MS, RD, CSCS
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