A blend of red grapes and green tea extracts combined with the amino acid L-carnitine is added to more expensive pet foods for older dogs and cats. And no doubt there are slimming supplements for humans on the market that also contain the mixture.
If you are a user of these products, you can breathe easy: according to Korean research, soon to be published in Phytotherapy Research, they are effective.
The time when researchers tested the effect of a single nutritional substance on fattened lab animals, in the hope of finding one that would make them lose weight and become healthier, is long gone. Although the studies often produce positive results, these often don’t work for humans. That's why scientists are now focusing on the effect of blends, and the Korean research is an example of this.
The Koreans took three nutrients known to be effective individually to see how they work in combination. L-Carnitine sluices fatty acids in cells into the mitochondria where they are converted into energy. If you read the textbooks, L-carnitine is as strong a supplement as creatine. But in practice it's not.
Extracts of green tea contain phenols like EGCG. These inhibit the breakdown of pep-hormones like adrenalin and inhibit the growth of fat cells. The Koreans' extract contained almost 60 percent EGCG.
Resveratrol, a phenol in red grapes, is a more effective fat-cell inhibitor than EGCG in test tube experiments, but in the body enzymes attach all kinds of sugar and sulphur groups to resveratrol really fast. And this may block the effect of the substance. The grape extract that the Koreans used consisted of 5 percent resveratrol.
Concentrating the carbohydrates in the evening meal resulted in a higher weight loss, as the table below shows. The control group lost five kg fat; the experimental group lost seven kg.
The ratio (in grams) of the grape extract-green tea extract-L-carnitine mixture was 1: 0.6 : 0.5.
The Koreans first gave young mice normal feed [CD] or feed containing extra sugar and fat [HFD] for three weeks. The HFD mice put on weight fast. Some of the HFD animals were then given 300 mg per kg bodyweight of the blend for eight weeks, through a feeding tube. Another group of the mice was given 1200 mg daily.
The blend almost halved the increase in weight in the fattened mice, and also inhibited the growth of fat reserves in the liver. The two doses were almost equally effective, but the higher dose reduced the concentration of ‘good' cholesterol, HDL.
The researchers speculate that the components in the blend have a mutually reinforcing effect on each other, but unfortunately they didn't measure the effect of the components individually.
Mice's metabolic rate is about 10 times higher than that of humans. If you divide the doses used in the experiment by 10 you'll get a rough yet conservative estimation of the doses that would be suitable for humans.
The study was sponsored by the Korean government.
Phytother Res. 2011 Apr 8. doi: 10.1002/ptr.3476. [Epub ahead of print]