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The anti-obesity effect of vitamin D and genistein combined

The modest fat-decomposition effect of high doses of vitamin D is enhanced in combination with genistein, the isoflavone in soya protein. Nutritionists at the University of Georgia discovered this when they exposed fat cells to both substances in test tubes.

Trials have shown that people lose weight a tiny bit faster when they have more vitamin D in their blood. In an 11-week experiment, fat people on a weight-loss programme lost 200 g more for every nanogram of vitamin D3 in one millilitre of their blood. However, there are also studies in which absolutely no slimming effect of vitamin D was detected.

In fact, it doesn't matter what substance you look at the effect of a single nutrient is nearly always disappointing. Nutrients are not the same as medicines. The focus of many research groups is therefore slowly shifting to studying the combined effect of several nutrients.

At the University of Georgia researchers are looking at the effect of mixtures of substances on the breakdown of fat cells. In 2008 Obesity published the results of a study in which they had examined the joint effects of genistein and vitamin D.

The figure below shows how an extreme concentration of 200 micromoles genistein kills adult fat cells.

A concentration as high as this would be impossible in the body. The second figure shows how the combination of several nanomoles of vitamin D and several micromoles of genistein reduces the amount of stored fat in growing fat cells.

The anti-obesity effect of vitamin D and genistein combined

The anti-obesity effect of vitamin D and genistein combined

The anti-obesity effect of vitamin D and genistein combined

The figures above reveal something about the mechanism behind the joint slimming effect of vitamin D and genistein [structural formula shown below]. The combination reduces the production of the 'fat sensor' PPAR-gamma [left] and boosts the production of the vitamin D receptor [right].

The researchers suspect that genistein sabotages enzymes that convert the active form of vitamin D into non-active forms. As a result, genistein raises not only the concentration of the vitamin but also its fat-cell inhibiting effect.

A litre of soya milk contains about 40-50 mg genistein, but no vitamin D. Perhaps that's an idea for food manufacturers: vitamin D enriched soya milk for people who want to lose weight. And lots more nutrients could be added to slimmers' soya milk. More on this tomorrow.

Obesity (Silver Spring). 2008 Mar;16(3):539-46.