Pyruvate can be made from glucose metabolism. It helps to provide energy through the Krebs Cycle (an energy cycle
of chemical and enzyme actions that produce ATP). ATP is what
powers your muscles during short powerful movements. There are some rat studies that have suggested that Pyruvate can increase resting metabolic rate and also increase fat burning. There are also various studies performed using human subjects as well.
But is it really all it's cracked
up to be? After all, there's all these claims that Pyruvate can
significantly reduce fat, prevent fat loss "yo-yo" effects,
reduce cholesterol and increase endurance. Sure, it works,
and studies have shown it to help reduce fat, but how effective
is Pyruvate? There have been various human studies of supplementing Pyruvate, testing for weight loss benefits and exercise enhancing benefits. However, there are some conflicting evidence with respect to just how effective Pyruvate really is.
While some studies did find it to help increase weight loss, the resulting differences weren't very significant. Some studies found evidence to suggest that Pyruvate supplements help to achieve fat loss, while other studies find no apparent benefit of using Pyruvate for improving body composition or improving exercise performance. So we'll discuss all of these here. As for Pyruvate side effects, it appears to be safe and well tolerated. Most common side effects of Pyruvate include stomach upsets, diarrhea, gas problems, and bloating.
Calcium Pyruvate Supplements for Weight Loss
As already mentioned, Pyruvate helps to provide energy in the form of ATP, which could potentially help enhance exercise performance, and there are some evidence to support its use as a weight loss supplement as well. So it's not surprising to read claims about using Pyruvate supplements to improve fitness and achieve weight loss. However, exactly how well Pyruvate works is still very much up to debate as there are numerous studies with conflicting results.
In one double blind, placebo controlled study, 26 individuals were given either a pyruvate supplement or a placebo group. All the subjects took part in 3 days per week exercise program lasting 6 weeks. At the end of treatment, the Pyruvate group has achieved 1.2kg loss in body weight, 2.5kg loss in body fat mass, and their body fat percentage improved from average 23% (pre-treatment) to 20% (after). The study concluded that consuming 6g of Pyruvate for 6 weeks along with mild exercises, helps reduce body weight and body fat.  Another study involved 14 obese women who were given a diet with or without pyruvate for 21 days. The Pyruvate subjects had greater weight loss (5.9kg vs 4.3kg for placebo). They also had greater fat loss (4.0kg vs 2.7kg for placebo). The results of this study suggests that Pyruvate helps to increase fat loss and weight loss. 
In another study conducted at the University of Tennessee Medical School, the effects of Calcium Pyruvate supplementation was tested for its effects on metabolic response and exercise performance. In this study, 32 females were given either 5g of calcium Pyruvate or a placebo twice daily, for 30 days. During this time, they also took part in an exercise program. The results found no significant differences between the treatment group compared to the placebo group. While the calcium Pyruvate group had gained slightly less weight and lost slightly more fat, the differences were not significant. The study concludes that pyruvate supplements does not affect body composition, and does not improve exercise performance. 
As you can see from the studies discussed above, there are some conflicting evidence. It would appear that Pyruvate does have merits and benefits as a weight loss supplement, where the studies had found measurable improvements in fat loss and weight loss. The third study, while it did not find the results significant, did also report some weight loss in the Calcium Pyruvate group. Overall, I think a case can be made for supporting its use and applications as a weight loss supplement.
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The effects of pyruvate supplementation on body composition in overweight individuals.
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Body composition, energy utilization, and nitrogen metabolism with a 4.25-MJ/d low-energy diet supplemented with pyruvate.Stanko RT, Tietze DL, Arch JE.SourceClinical Nutrition Unit, Montefiore University Hospital, Pittsburgh, PA 15213.
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Effects of calcium pyruvate supplementation during training on body composition, exercise capacity, and metabolic responses to exercise.Koh-Banerjee PK, Ferreira MP, Greenwood M, Bowden RG, Cowan PN, Almada AL, Kreider RB.SourceDepartment of Preventive Medicine,