Pyruvate: just the facts

Every year a new batch of weight-loss products is touted to melt off excess pounds and increase muscle mass with minimal effort. This year is no different. One thing that's new, however, is that one new weight-loss product actually has scientific studies published in reputable journals that are alleged to back up its claims. The product is called pyruvate.

As promoted in healthfood stores and in radio commercials, scientific evidence is supposed to show that pyruvate can:

* Enhance weight loss by 37% over dieting alone

* Enhance fat loss by 48% over dieting alone

* Decrease appetite

* Increase muscle endurance

* Inhibit the regaining of fat once dieting stops

* Increase metabolism

Pyruvate (also known as pyruvic acid) is a three-carbon compound generated as the end product of glycolysis, one of the body's energy-generating pathways. During the early 1980s, research showed that pyruvate could prevent fatty buildup in rat livers from chronic alcohol use. It was probably these studies that inspired University of Pittsburgh researcher Ronald Stanko to investigate whether pyruvate might also work as a weightloss product. To date, Stanko is responsible for practically all of the studies on pyruvate and also holds the U.S. patent on "Pyruvate +," a form of pyruvate sold through Med Pro Industries.

The vast majority of studies done on pyruvate have in reality been mixtures of pyruvate and dihydroxyacetone, another three-carbon metabolite formed during glycolysis. Dihydroxyacetone is also found in over-the-counter pyruvate formulations but is rarely mentioned on the labels.

Science and Wishful Thinking

How well, though, does scientific research support the claims made for pyruvate?

Claim #1: Enhances weight loss. There are few studies on pyruvate and its effects on weight loss. Those that have been done suggest that pyruvate works under laboratory conditions, but its effect is not very impressive. In one study, for example, obese women (defined as weighing over 200 pounds) added 30 grams of pyruvate to a 1000-calorie/day liquid diet for 21 days. This resulted in 37% more weight loss and 48% more fat loss compared to control subjects who were on the 1000-calorie/day diet only (American Journal of Clinical Nutrition 56:630-635, 1992).

These figures seem impressive until one looks at the actual pounds of weight and fat lost. Specifically, the 37% enhancement in weight loss amounts to an average of only 3.5 pounds difference between the group taking the pyruvate and the one not taking it. With respect to the 48% increase in fat loss, this too is misleading because only 3.2 pounds more fat were lost in those consuming pyruvate.

In a second study, obese women were placed on a 500-calorie/day diet for 21 days, with some of the women supplementing with 16 grams of pyruvate and 12 grams of dihydroxyacetone (American Journal of Clinical Nutrition 55:771-776, 1992). Again, women supplementing with pyruvate did lose significantly more fat and weight than those not supplementing, but those using pyruvate lost an average of only 1.98 pounds more weight and 1.76 pounds more fat. It's important to note that these weight-loss studies took place under controlled laboratory conditions. No published peer-reviewed study to date has ever been conducted in real-life situations where calorie intake is not strictly controlled.

Claim #2: Decreases appetite. This claim is based on only one study--a study that was performed not on humans but on laboratory rats. In this investigation, laboratory rats were allowed to eat as much food as they wanted. At the end of the study, researchers found that the rats that received pyruvate and dihydroxyacetone consumed less food than rats not receiving the supplements (Journal of Clinical Nutrition 53:847-853, 1991). To date, however, such a study has never been performed on humans.

Claim #3: Increases muscle endurance. There is only one published peer-reviewed study suggesting that pyruvate can increase muscle endurance--and the only published study done on men (Journal of Applied Physiology 6811]: 119-124, 1990). This is the study that is most quoted to people interested in increasing their exercise ability. The study showed that a mixture of 25 grams of pyruvate and 75 grams of dihydroxyacetone taken for 7 days increased triceps endurance by 20%.

Of course, until other studies are done, this study should be considered preliminary. What's more, this study did not look at traditional aerobic conditioning like jogging or bicycling but rather at how long the triceps muscle (on the back of the upper arm) took to totally exhaust itself. Muscles other than the triceps as well as those undergoing different types of exercise might react differently, so it's unknown how these results might translate over to exercising individuals. This problem is even mentioned in the study in light of the fact that one of the participants had a reduced triceps endurance capacity following ingestion of pyruvate. Therefore, individuals looking to pyruvate to enhance their exercise ability should save their money until more research is conducted in this area.

Claim #4: Inhibiting the regaining of fat once dieting stops. Everybody knows that when one stops dieting and goes back to old eating habits, that weight slowly creeps back. Anything that could slow this process would certainly appeal to dieters who fall off the wagon. But the claim that pyruvate can suppress appetite is based on only one published peer-reviewed study (International Journal of Obesity 20:925-930, 1996).

In this investigation, obese women (average weight 228 pounds) went on a 310-calorie/day diet for 21 days. Following this, they then went on a three-day high-calorie diet to purposely regain the weight. Some women used a mixture of 15 grams of pyruvate and 75 grams of dihydroxyacetone during the dieting process. After the study, it was found that those women who didn't receive any pyruvate regained an average of 6.38 pounds of weight, while women who used pyruvate regained an average of 3.96 pounds of weight. This amounts to only a 2.42-pound difference between the groups. With respect to the regaining of fat, women not using pyruvate regained an average of 3.96 pounds of fat while those using the pyruvate regained an average of 1.76 pounds of fat. Again, this amounts to only a 2.2-pound difference between them.

Claim #5: Increases metabolism. Much hype surrounds the claim that pyruvate can increase one's metabolism and therefore help one lose weight. Unfortunately there is no solid evidence to support this claim. Earlier studies in rats did show that pyruvate increased resting metabolism (the number of calories used at rest), but these results have never been confirmed in human studies. In fact, in the most recently published pyruvate study, the group of people who did not receive pyruvate had a higher resting metabolism at the end of the study than those who did receive the pyruvate. Therefore, the idea that pyruvate enhances human metabolism remains speculative at best.

With respect to side effects, the literature to date seems to show that pyruvate is relatively safe with the most noticeable problems being occasional diarrhea, loose or softened stools, and a rumbling sound in the gut which is caused by gas passing through the intestines. At the present time, nobody is sure of the physiological mechanism of action of the pyruvate/dihydroxyacetone mixture and how it relates to weight loss or any other reported claim.

All of the published peer-reviewed studies done to date except one have been either conducted on obese women on very restrictive diets or on laboratory rats. Therefore, results obtained from these populations may not indicate what would be gained from humans under more real-life situations where food intake is not strictly controlled. Also, the subjects in the studies consumed very large amounts of pyruvate and dihydroxyacetone, far in excess of the dose of 3 to 5 grams per day recommended in over-the-counter products. To date, no published peer-reviewed research exists showing that the 3- to 5-gram dose will produce the same effects as the higher dosages used in the studies.

Popular Hype

One prominent false claim that one is likely to encounter is "pyruvate is backed up by 25 years of extensive scientific research" (J. B. Roufs, Muscle and Fitness, December 1996). While it's true that research on pyruvate does appear in prestigious scientific journals, the fact is that there were no studies on pyruvate and weight loss published before 1986 or after 1996. That's only 10 years, not 25. Furthermore, if one were to look just at the human studies using pyruvate, then this number is even further reduced to only six years.

Some people selling pyruvate give out free audiotapes that boast of pyruvate's supposed amazing abilities. In one of these tapes, the person selling pyruvate (who is identified as a physician) states that when you are using pyruvate, "You are in the fat-burning mode--even when you are not exercising." This is very interesting because when you are resting, you are already in the "fat-burning mode." At rest, approximately 70% of the calories you derive energy from are coming from fat with the remaining 30% coming from carbohydrates (sugars).

Some people claim that pyruvate is an antioxidant. As is mentioned in a recent review of pyruvate in Medicine and Science in Sport and Exercise (30: 837-843, 1998), some evidence hints that pyruvate might act as an antioxidant. But only three studies show that pyruvate acts as an antioxidant--and these studies were conducted not on humans but on rodent hearts. More research is necessary to determine the efficacy of pyruvate's antioxidant action in humans.

Claims that pyruvate aids in cardiac function are prevalent. But there is absolutely no published peer-reviewed evidence that either pyruvate or dihydroxyacetone aids the heart in pumping blood more effectively. In fact, those studies that did record pyruvate's effect on heart functions found no change after use. Therefore, if you have any cardiac abnormalities, pyruvate is not the answer to your problems. You are best served by following medical advice.

Pyruvate is also supposed to build muscle. There is no published peer-reviewed scientific evidence showing that pyruvate can build muscle tissue. In the only study of exercise and pyruvate ever conducted, no mention was made regarding pyruvate having any effect on muscular strength or hypertrophy. This claim seems to be specifically targeting those individuals interested in weight lifting and bodybuilding.

Joseph P Cannon is an exercise physiologist and an NSCA-certified personal trainer.

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