Casein or Whey Protein: Which Protein Is Best for Long-Term Fat Loss?

An effective approach to weight loss is to increase dietary protein or lower the ratio of carbohydrate to protein in the diet. A low carbohydrate-to-protein ratio (<2) with greater than 100 grams of protein per day in the form of meat, eggs, cheese, milk and nuts has been shown to increase fat loss and retain lean muscle during dieting.1-3 Different protein (whey and casein) has different physiological effects on the body. Fast proteins, such as whey protein, are soluble, whereas slow proteins, such as casein, clot in the stomach. Slow proteins can delay gastric emptying and result in lower but more sustained plasma amino acid elevations after ingestion, which may be associated with differences in hormonal and thermogenic responses.

On the basis of their absorption pattern, dietary proteins can be divided into ‘fast’ and ‘slow’ digestible proteins. For example, whey proteins modulate several hormones that influence body composition. Acute ingestion of whey protein has been shown to significantly lower hyperinsulinemia (less lipogenesis— less fat-storage potential), lower cortisol levels (lean muscle preservation) and increase ghrelin release (satiety enhancement).

Based on acute studies, whey protein seemed superior to casein for weight loss. Two human studies conducted at the University of Surrey in England compared the acute effects of whey and casein (another milk-based protein) on appetite and satiety-related hormones, including cholecystokinin. In the first study, participants consumed a liquid meal containing equivalent amounts of either whey or casein. Ninety minutes later, both groups were allowed to eat freely at a buffet. The whey group consumed significantly fewer calories. Compared to the casein drink, the whey beverage produced a 28 percent increase in plasma amino acid concentrations over 3 hours, and a 60-65 percent increase in two hormones associated with satiety, cholecystokinin and glucagon-like peptide-1. The whey group also reported a greater sense of fullness and satisfaction than the casein group.4 Whey protein may be superior to casein for weight loss; however, long-term studies comparing the two have yet to be examined.

Whey Versus Casein Over 12 Weeks: Which Is Better?

Researchers from the Netherlands compared the effects of different types of protein (whey and casein) on weight loss. Forty-eight subjects consumed protein during an energy restriction period of five to six weeks, followed by a weight maintenance period of 12 weeks. During weight maintenance, subjects were assigned to a high-protein casein group or a high-protein whey group. Each group consumed 50 grams of protein daily— two doses a day (25 grams total) of protein, either casein or whey. The subjects were instructed to maintain their normal daily activities while adhering to their diet. At the end of the 12 weeks, there was no difference in weight loss or change in hip circumference between the casein and whey groups. The only physiological difference was improvement in LDL/HDL ratio for the casein-protein group.

Differences in protein blends need to be examined further to determine if different whey proteins (isolate, hydrosylate, etc.) have different effects on weight loss. Many of the positive studies examining the effect of whey protein have been acute studies, but this study found that long-term, there is no difference between casein and whey protein for long-term weight loss.5 High-protein diets have long been shown to enhance weight loss, but it may not matter whether it’s a fast- or slow-digesting protein. Based on the study, both proteins worked equally for weight loss. Further studies need to examine different types of whey protein and their relation to weight loss.


1. Layman DK, Boileau RA, Erickson DJ, Painter JE, Shiue H, Sather C, Christou DD: A reduced ratio of dietary carbohydrate to protein improves body composition and blood lipid profiles during weight loss in adult women. J Nutr, 2003, 133:411-417.

2. Layman DK, Baum JI: Dietary protein impact on glycemic control during weight loss. J Nutr, 2004, 134:968S-73S.

3. Noakes M, Keogh JB, Foster PR, Clifton PM: Effect of an energy-restricted, high-protein, low-fat diet relative to a conventional high-carbohydrate, low-fat diet on weight loss, body composition, nutritional status, and markers of cardiovascular health in obese women. Am J Clin Nutr, 2005, 81:1298-1306.

4. Hall WL, Millward DJ, Long SJ, Morgan LM. Casein and whey exert different effects on plasma amino acid profiles, gastrointestinal hormone secretion and appetite. Br Nutr, 2003 Feb;89(2):239-48.

5. Claessens M, van Baak MA, Monsheimer S, Saris WH. The effect of a low-fat, high-protein or high-carbohydrate ad libitum diet on weight loss maintenance and metabolic risk factors. Int J Obes, (Lond), 2009.


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