Dairy Helps Dieters Maintain Muscle While Losing Fat

Written by: Lauren Milligan Newmark, Ph.D. | Issue # 41 | 2015

If you have ever been on a diet, chances are you own a scale. From contestants on popular weight loss reality shows to at-home dieters, the scale is used as an indispensable tool for measuring dieting success. Unfortunately, those changing numbers on the scale only tell part of the story. Successful weight loss is not just about losing body mass, but about losing fat mass while preserving lean muscle mass. So, what is the secret to success? Dieters eating more protein and fewer carbohydrates have been shown to maintain muscle while dropping fat (1), and a growing number of studies are finding that increased consumption of whey proteins from dairy promotes even greater fat loss and lean muscle preservation (2-5). If you also take into account calcium’s positive effects on fat metabolism, there is great potential for dairy to really tip the scales in a dieter’s favor.

Lose the fat, keep the muscle

The National Institutes of Health estimates that over 70% of American adults are overweight (having a body mass index or BMI of 25.0 – 29.9), or obese (BMI > 30.0). While much research has gone into understanding potential genetic factors that predispose individuals to obesity (6), solutions for this epidemic must certainly come from behavioral modifications, particularly with regard to diet.

Reducing energy (caloric) intake is obviously an important component of weight loss. After all, in order to lose weight you need to expend more energy than you take in. But simply cutting calories to get to an ideal number on the scale is a very shortsighted and ineffective approach. Instead, clinicians advise that weight loss should focus on reducing fat mass while preserving lean body mass (i.e., muscles) in order to improve the metabolic health of the individual (1-5, 7). Maintaining lean body mass while dropping fat results in an increased basal metabolic rate (BMR), because muscle tissue is more metabolically expensive than fat. A body that is more expensive to run can burn calories more efficiently and has a better chance of keeping the fat weight off, preventing the yo-yo effect that is so common with many diets. In addition, improving the proportion of lean to fat tissue in the body positively influences glucose metabolism and the regulation of blood sugars (1, 3, 7). While the numbers will not go down as quickly (muscle is heavier than fat), the end result is a more metabolically healthy individual.

When someone looking to lose weight reduces their energy intake without regard to macronutrient intake (the proportion of carbohydrates, protein, and fat), they run the risk of losing both muscle and fat. This is because the body responds to energy reduction by decreasing the rate of muscle protein synthesis—a very costly physiological process. Increasing the consumption of dietary protein is integral to keeping the muscle making machinery in the “on” position.

Diets that trade some carbohydrate calories for calories from protein are effective at maintaining lean tissue during weight loss (1). But not all dietary proteins are as successful in maintaining (or growing) lean body tissue. Amino acids, the chemical building blocks of protein, are biologically active and can differentially influence the rate of protein synthesis. For example, the branch chain amino acid leucine is known to act as a chemical signal directly on the nuclei inside of muscle fibers —promoting muscle growth and also preventing muscle breakdown more effectively than other amino acids. Keeping lean muscle, then, is not only about eating a sufficient amount of protein, but also about eating the right proteins.

Dairy’s special ingredients

Although leucine is found in several dietary sources, including eggs, fish, beef, and chicken, the highest concentration comes from the whey fraction of milk. Whey protein has more than twice the leucine than other protein sources, and so it is no surprise that it has been a primary focus of dietary intervention studies on overweight and obese individuals (2-5, 7, 8).

But dairy’s whey proteins do more than stimulate muscle protein synthesis. Leucine is hypothesized to inhibit fat cell production (lipogenesis) and facilitate fat cell breakdown (lipolysis). Currently, these two effects have been demonstrated conclusively only in in vitro studies (2). In addition, leucine and other amino acids found in whey influence hormones related to fat and muscle metabolism, as well as appetite. For example, whey protein lowers serum cortisol levels, which can augment the preservation of muscle tissue (4). Whey also acts on ghrelin, the so-called hunger hormone, produced by the stomach when it is empty. Lower circulating levels of ghrelin act to enhance satiety (feeling full). Baer et al. (8) found that study subjects that are supplemented with whey protein had lower levels of circulating ghrelin compared to those supplemented with soy or carbohydrates. Therefore, while consuming proteins can make people feel more full in general, whey protein is believed to have an even greater influence on appetite, which can be especially important for individuals trying to stick to an calorie restricted diet.

In addition to whey proteins, dairy is one of the best dietary sources of calcium. Numerous lines of evidence support the hypothesis that increased dietary calcium positively influences fat loss. Increasing dietary calcium is believed to positively influence how dietary fat is absorbed and metabolized directly following a meal. In contrast, diets low in dietary calcium are associated with decreases in lipolysis and increases in lipogenesis (9). These findings suggest that calcium, like leucine, may help direct the body to burn up fat cells as opposed to lean tissue an energy source (reviewed in 5).

Putting dairy to the test

Despite these known functions of whey and calcium in muscle maintenance and fat metabolism, there are only a handful of studies that have directly investigated dairy’s affect on body composition during weight loss. For example, in a 2012 meta-analysis, Abargouei et al. (5) found only 14 randomized control trials that looked at dairy and weight loss, and of these only six collected data on changes in lean body mass. The meta-analysis from the data on weight loss, which represented nearly 900 overweight or obese adults, found that increasing dairy intake to simply meet the recommended daily requirements (3 servings) while on a caloric-restricted diet was associated with significantly greater weight loss than conventional low calorie diets (5). Of the studies that considered lean body mass changes, the meta-analysis identified an average gain of 0.58 kg in lean mass in individuals randomized into the higher dairy groups. Interestingly, the effects of dairy were only significant when accompanied by energy restriction. The positive effects of dairy on fat loss and muscle preservation may be more pronounced when changes are made to daily caloric consumption (5).

One of the biggest issues identified by Abargouei et al.’s systematic review was the variation in experimental variables. Some studies increased dairy consumption, but not the proportion of calories coming from protein, while others did both. This makes it difficult to conclude with certainty whether the positive weight loss effects are from higher dairy intake alone, or higher dairy intake alongside increased protein consumption. Josse et al. (2) tackle this problem by randomizing their subjects (90 overweight or obese premenopausal women) into one of three groups: high protein/high dairy (30% of calories from protein, 6-7 serving of dairy per day), adequate protein, adequate dairy (15% of calories from protein, 3-4 servings of dairy), and adequate protein, low dairy (15% of calories from protein, 0-1 servings of dairy). In the adequate protein groups, 55% of the calories were carbohydrates and 30% fat; in the high protein group, carbohydrate energy was reduced to 40%. All groups underwent the same caloric restrictions (- 500 kcal/d from their pre-study diet) and daily exercise regimen (designed to burn off an additional 250 kcal/d). Using body composition data collected at weeks 0, 8, and 16 by duel-energy X-ray absorptiometry (DXA), Josse et al. (2) found the high dairy/high protein subjects had the greatest gains in lean tissue as well as the greatest fat loss. And while lean body mass was maintained in the adequate protein/adequate dairy group, the low dairy group actually lost lean mass. These findings suggest that even under conditions of adequate protein intake, caloric restriction accompanied by low dairy intake can result in muscle turnover rather than muscle preservation.

Josse et al. also utilized MRI scans to assess changes in visceral adipose tissue (VAT) over the course of the study period. Higher amounts of VAT, particularly that located in the trunk, are associated with several health risks, including cardiovascular disease and type 2 diabetes, and therefore many weight loss studies are particularly interested in identifying methods for targeting VAT. In all of the groups, changes in VAT correlated with intakes of protein and calcium; the more protein and calcium consumed, the greater the loss in VAT. Moreover, DXA scans showed greater changes in trunk fat in the high protein/high dairy group compared to the other two study groups. Not only did the increased protein and dairy intake favor fat over muscle as an energy source, it targeted the very fat stores that are most detrimental to the individual’s metabolic health.

Fad or fact?

It seems like every week there is a new fad diet being advertised to provide quick results with little effort—those “eat all you want and still lose weight” ads. Is the “dairy diet” simply the latest fad? The handful of studies that have looked at dairy consumption and body composition certainly do not suggest that fat loss will come quickly, or without effort (participants still had to cut calories and exercise daily). And the repeated finding of greater fat loss and preservation (or even increases) in lean body mass with increased dairy intake most certainly moves dairy from “fad” status squarely into “supported by experimental data” status. Fad diets are not going to solve the obesity problem in the U.S. and across the globe. The focus must be on dietary modifications that influence long-term changes in body composition rather than short-term changes on the scale. And dietary modifications that are easily implemented, such as consuming the recommended daily intake of dairy, have the greatest potential for being successful.

References

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