Supplementing with whey protein found to improve body fat levels compared to carbohydrate

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While protein supplementation can conjure up images of body-building and athlete’s looking to generate power, there is some evidence that it might help mere mortals too. There is quite a body of evidence which suggests, for example, that a bit more protein in the diet can assist with weight loss and weight loss maintenance. See here, here and here for some examples of relevant science.

I was interested to read a recent study which assessed the effect of protein supplementation on weight and other measures, by comparing it to supplementation with carbohydrate. 73 overweight or obese adults were treated with one of three supplements [1]:

  1. whey protein
  2. soy protein
  3. carbohydrate (maltodextrin)

Each supplement provided 400 calories of energy. The supplements were divided between breakfast and dinner. The individuals were instructed to take the supplements but were not advised to make any changes to their diet. The trial lasted 6 months.

Here’s what the results showed:

  • Compared to the carbohydrate-supplemented group, those taking the whey protein supplement were an average of 1.8 kg lighter.
  • Compared to the carbohydrate-supplemented group, those taking the whey protein supplement ended up carrying 2.3 kg less fat.
  • Compared to the carbohydrate-supplemented and soy-supplemented groups, those taking the whey protein supplement ended up with smaller waist circumferences.
  • There were no significant differences between the results seen by those taking soy protein and carbohydrate supplements.

In short, compared to carbohydrate supplementation, whey protein improved weight body fat and waist circumference (larger waist circumference is associated with an increased risk of disease and death).

Before we attempt to explain these differences, it’s worth noting that the addition of the supplements appeared to be compensated for, to a large degree, by consumption of less in terms of the individuals’ normal diets. 400 calories a day equates to 64,000 calories over 23 weeks. There are about 3,500 calories in a pound of fat so, theoretically, the weight gain without any compensation would be around 18 lbs (about 8 kg). This did not happen. Basically, the results showed that the carb group saw a modest increase in weight and body fat, while the whey-supplemented group saw a modest decline in these measures (the soy group pretty much stayed the same).

One obvious explanation for this finding is that whey protein was more satisfying, and led to individuals more than compensating for the addition energy from the supplement in terms of reduced eating of other foods. Consistent with this is the fact that the whey-taking group were found to have lower levels of the appetite-stimulating hormone ghrelin compared to both the other groups.

However, logging of the diets (admittedly not assured to be 100 per cent accurate) revealed the average daily calorie intakes to be:

  1. whey supplemented group – 2183 calories
  2. soy supplemented group – 2267 calories
  3. carbohydrate supplemented group – 2164 calories

So, it does not seem as though the whey-supplemented group ate any less than the carb-supplemented group. Physical activity was monitored, and was found to be the same across the groups.

So, what else might explain the findings? It’s been found that higher protein diets can stimulate the metabolism, and this effect may be mediated through levels of thyroid hormones. There was evidence of this in this study, but most apparent benefit was seen in the group supplemented with soy, suggesting that the better outcomes in the whey group were not largely down to this mechanism.

One other potential explanation for the results concerns the impact of whey and maltodextrin on hormones that control fat stores in the body, especially insulin. Insulin is a hormone that encourages fat deposition. In the protein-supplemented groups, insulin levels were a little lower compared to those in the carb-supplemented group.

The other thing worth bearing in mind is that while protein (like carbohydrate) does stimulate insulin secretion, it also induces he secretion of another hormone too by the name of glucagon. One of glucagon’s effects is to stimulate the release of fat from the fat cells. Also, unlike insulin, glucagon does not stimulate the uptake of sugar into the body’s cells. This helps restrict the amount of glucose available for the production of something called glycerol that is required for the ‘fixing’ of fat in the fat cells.

In other words, while protein increases insulin secretion, the rise in glucagon that comes at the same time mitigates the fat-forming effects of insulin. With carbohydrate, we get insulin secretion that is unopposed by glucagon, with great fat-forming potential to boot.

This study should serve to remind us that the impact that different types of calories have on body fat stores can be different. It also demonstrates that it can be possible to lose fat through a change in dietary composition but without any conscious restriction of calories.


1. Baer DJ, et al. Whey protein but not soy protein supplementation alters body weight and composition in free-living overweight and obese adults. J Nutr. 2011;141(8):1489-94

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