On Whey Protein, Insulin Spikes and Losing Fat

Some argue against the use of whey protein when you’re trying to lose fat, mainly on the basis that it raises insulin levels.

“Whey is a fast protein that spikes insulin,” they say. “Every time you chug down a whey protein shake, there’s a big insulin response, and fat burning is stopped dead in its tracks. If you want to lose fat, stop using whey.”

It’s true that whey is a highly insulinogenic food, which means that it triggers a large release of insulin after you eat it. In fact, whey has a much bigger impact on insulin levels than even pure glucose.

But this has little to do with changes in blood sugar levels. Rather, the amino acids in whey trigger insulin secretion directly in pancreatic beta cells. The branched-chain amino acids, leucine in particular, appear to be the most potent insulin secretagogues.

Whey also stimulates the release of a couple of gastrointestinal hormones known as GIP and GLP-1, both of which have the effect of raising insulin levels.

Should you stop using whey if you want to lose fat?

Whey comes from milk. Around 20 percent of milk protein is whey, with the remaining 80 percent coming from casein.

So if the “whey prevents fat loss” claim was true, you’d expect to see a slower rate of fat loss in people eating large amounts of dairy produce like milk and yogurt.

In one study, researchers compared low (0–1 serving of dairy per day), medium (3–4 servings of dairy per day) and high (6–7 servings of dairy per day) dairy diets.

All three diets were set up so that the women taking part consumed around 500 calories less than they needed to maintain their weight.

After 16 weeks of diet and exercise, all three groups lost weight. If whey or dairy had a negative impact on weight loss, then you’d expect it to show up in this study. But it didn’t.

The results show “no significant difference” in weight loss, which averaged almost 10 pounds across the three groups.

These are the results from a single trial, and it’s a mistake to draw definitive conclusions about anything based on the findings of one study. But the results certainly don’t contradict a sea of existing data on the subject. In fact, there’s plenty of research out there showing much the same thing.

• When 50 overweight adults were assigned to a diet that derived roughly one-third of its calories from protein, either largely from dairy products or mixed sources, there was no significant difference in weight loss between the groups over 12 weeks (dairy, -19.8 pounds; mixed, -20.5 pounds).
• In a 6-month trial at the University of Vermont, 54 obese adults were assigned to either a high- or low-dairy diet. There was no significant difference in fat loss between the groups (high-dairy, -22 pounds; low-dairy, -20 pounds).
• A study in the Journal of Obesity found no difference in fat loss between low-dairy (no more than 1 serving of dairy per day) and adequate-dairy (3-4 servings of dairy per day) diets over a 12-week period (adequate-dairy, -11 pounds; low-dairy, -11 pounds).

Researchers from the Netherlands have also looked at the effects of different types of milk protein (whey and casein) on 12 weeks of weight maintenance following a 6-week period of weight loss.

During the weight maintenance phase of the study, subjects were assigned to either a casein or a whey group. Each group consumed 25 grams of the supplement twice a day.

Again, if whey was making it harder to burn fat, you’d expect to see the whey group having more trouble maintaining their weight.

Yet the results show no significant difference in terms of fat loss between the casein and whey groups.

In fact, the whey group actually lost a little more fat during the weight maintenance phase (- 5 pounds) compared to the casein group (- 3.5 pounds).

Subjects taking whey also gained more fat-free mass (3 pounds) than those given casein (0.4 pounds). But the differences were not large enough to reach statistical significance.

Yes, whey does stimulate the release of insulin. But despite the endless pontificating that goes on whenever a study comes out showing that food A stimulates the release of hormone B, the short-term response of a single hormone to a single food doesn’t really tell you anything useful.

In short, there is no good reason to believe that whey slows fat loss, and no reason to avoid it if you’re trying to lose fat.