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September 2006, FitnessRx for MEN

Ultimate Nutrition: How Whey Protein Promotes Fat Loss
By Susan M. Kleiner, PhD, RD, FACN, CNS, FISSN

You have read many articles in the pages of FitnessRx for Men that have told you about the weight control and fat-loss benefits of having plenty of calcium in your diet. Each time we’ve told you that story, you’ve learned that subjects supplementing with calcium have lost more body fat compared to those eating the same amount of calories, but without adequate calcium in their diets. At the same time, we’ve also said that when subjects were given dairy foods as their source of calcium (three servings per day), they lost even more weight compared to the group given calcium supplements. Recent research on whey protein, the primary protein in dairy foods, may be opening the door to our understanding of why this happens.

Calcium + ? = Fat Loss

Studies investigating the influence of calcium on fat loss began in earnest in 2000, when a group of researchers looked at some dietary data from clinical hypertension trials and noticed that the group that had more calcium in their diets lost body fat, despite eating the same number of calories as the group without the added calcium.1 Since that time, many studies have been conducted testing the calcium theory and the biochemical mechanisms explaining how calcium influences fat metabolism. However, almost every time dairy products are used as the dietary calcium source, those subjects lost more fat compared to the group using calcium supplements alone to raise their dietary calcium levels, despite eating the same number of calories. The calcium-fat metabolism mechanism has never been able to account for all the fat lost by subjects when dairy foods are used as the source of added calcium in the diets of subjects. In fact, the mechanism can usually account for only about half of the weight loss. So, scientists have been investigating the other prominent parts of dairy foods that may influence weight loss and whey protein has become a primary suspect.

Burning Fat and Building Muscle

Whey protein is unique as it’s only found in dairy foods. Compared with other proteins, whey protein is high in the branched-chain amino acids (leucine, isoleucine and valine). This particular group of amino acids not only supports protein synthesis in general, but plays specific metabolic roles in energy metabolism during exercise and the building of muscle proteins. Only diets that provide more than enough branched-chain amino acids, and leucine in particular, can shift energy away from manufacturing fat to building more muscle.

Very exciting animal research being conducted in Tokyo, Japan, by Masashi Morifuji and colleagues has discovered that in exercising rats, whey protein inhibits fat production in the liver and enhances fat synthesis in muscles. This means less fat stored in the body and more fat available as energy during exercise. They have also found that whey protein increases carbohydrate storage in the liver and muscles of exercising rats, again, allowing more fuel for longer and more intense exercise. The investigators suggest that both these factors may be attributable to the distribution of amino acids in whey protein, but the actual mechanisms aren’t yet understood. If this finding can be reproduced in humans, then it’s possible that including dairy products and supplementing with whey protein would not only enhance exercise endurance, but also assist with fat loss in individuals who exercise.2,3

Dairy also contains a number of bioactive compounds that may work together with the amino acids and calcium to enhance fat burning. The enzyme angiotensin II enhances the synthesis of fats in adipose tissue. Whey contains angiotensin-converting enzyme (ACE) inhibitory activity, meaning that it inhibits the activity of angiotensin II, slowing or turning off fat synthesis in adipose tissue. When added all together, whey protein and dairy foods have quite a unique package to slow down fat synthesis and stimulate fat burning and muscle building.4

Hunger and Appetite

High-protein diets have become popular in part due to the appetite-suppressing effects of higher protein in the diet. Protein stimulates the secretion of a number of hormones involved in satiety and appetite, including cholecystokinin, insulin, leptin, glucagon-like peptide 1 and others. So, adding more protein to the diet, in any form, may help control hunger and appetite. Whey protein may be a particularly powerful protein when it comes to stimulating the satiety hormones.

Two studies conducted in England, comparing the influence of whey and casein (another milk-based protein) on appetite and satiety-promoting hormones, have found whey to have a greater influence on appetite suppression and satiety. After consuming a liquid meal containing either whey or casein, subjects in the first study were allowed to eat as they liked from a buffet served 90 minutes later. Those who had consumed the whey beverage at significantly fewer calories compared to the casein group.5

During the second study, the researchers gave the same liquid test meals, but measured blood levels of amino acids and satiety-related hormones. Compared to the casein beverage, the whey drink produced a 28 percent increase in plasma amino acid concentrations over three hours, a factor alone associated with increased satiety. They also found a 60 to 65 percent increase in cholecystokinin and glucagons-like peptide 1, two hormones associated with satiety. The whey groups reported a greater feeling of fullness and satisfaction than the casein group. So, it appears that proteins are not all alike in their abilities to enhance satiety and suppress appetite – and whey may be a standout when it comes to feeling and staying full and satisfied.

In the Mood

People who have had an episode of depression have increased odds of developing a cluster of conditions including abdominal obesity, high blood pressure, elevated blood sugar and unhealthy cholesterol levels. Commonly referred to as Metabolic Syndrome, these conditions set the stage for type 2 diabetes, heart disease and stroke. Conversely, studies also show that obesity increases the risk for depression. So, once you’re overweight you have a greater chance of becoming depressed, which may thwart any efforts you make to improve your lifestyle and lose weight: a vicious cycle.

Changes in emotional state are initiated in the brain. Chemicals called neurotransmitters control communication between brain cells and connect the circuits and structures of the brain to elicit mood states. Depression is believed to be due to either the low availability and/or dysfunction of neurotransmitters. Serotonin is the most significant and well-understood neurotransmitter. When levels of serotonin drop, mood is depressed. When serotonin can’t act effectively to allow for cell-to-cell communication, symptoms of depression rise. Drugs like Prozac and Effexor XR increase serotonin concentrations in the brain, improving mood and reducing depression.

Tryptophan, an amino acid, is the chemical precursor to serotonin. The production of serotonin in your brain is limited by how much tryptophan is available in your bloodstream. Since tryptophan is an amino acid, it’s found in protein-containing foods. But only certain foods are especially high in tryptophan and have been shown to elevate blood levels of tryptophan and brain levels of serotonin.

Studies on subjects who are prone to the effects of stress have investigated the impact that diets high in whey protein, a naturally rich source of tryptophan, have on their stress response, mood and cognitive performance. The results of two studies have shown decreased physiological responses to stress, improved mood and memory performance as a result of increased brain tryptophan, and serotonin activity from a diet high in whey protein. Although the healthy subjects who were not overly prone to stress didn’t gain the same level of benefit, it seems clear that even mildly depressed individuals could benefit from this small dietary change.

All in a Glass of Milk

The first thing many men do when they decide to start a fat-loss diet is cut out milk. It’s always been viewed as an easy way to cut out a few hundred calories that you would, in all likelihood, never miss. After reading this article, I hope you’ll never think that way again. In fact, adding three servings each day of low-fat and nonfat milk, yogurt, cottage cheese and dairy beverages like kefir aren’t only healthy for your body and mind and give you energy to exercise, they’ll likely enhance your weight-loss efforts. Whey to go!


  1. Zemel MB, Shi H, Greer B, DiRienzo D, Zemel PC: Regulation of adiposity by dietary calcium. FASEB J, 14:1132-1138, 2000.
  2. Morifuji M, Sakai K, Sanbongi C, Sugiura K. Dietary whey protein downregulates fatty acid synthesis in the liver, but upregulates it in skeletal muscle of exercise-trained rats. Nutrition, 21:1052-1058, 2005.
  3. Morifuji M, Sakai K, Sanbongi C, Sugiura K. Dietary whey protein increases liver and skeletal muscle glycogen levels in exercise-trained rats. Br J Nutr, 93:439-445, 2005.
  4. Zemel MB. The role of dairy foods in weight management. J Am Coll Nutr, 24:537S-546S, 2005.
  5. Hall WL, Milward DJ, Long SJ, Morgan LM. Casein and whey exert different effects on plasma amino acid profiles, gastrointestinal hormone secretion and appetite. Br J Nutr, 89:239-248, 2003.
  6. Markus CR, Olivier B, Panhuysen G, Gugten J Van De, Alles M, Westenberg H, Fekkes K, Koppeschaar H, De Haan EHF. The bovine protein Alpha-Lactalbumin increases the plasma Trp/LNAA, and in vulnerable subjects it raises brain serotonin activity, reduces cortisol concentration, and improve mood under stress. Am J Clin Nutr, 71:1536-1544, 2000.
  7. Markus CR, Olivier B, de Haan EHF. Whey protein rich in alpha lactalbumin increases the plasma Trp/LNAA ration, and improves cognitive performance in stress-vulnerable subjects. Am J Clin Nutr, 75:1051-6, 2002.
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