Fruit has been shown to have anti-obesity effects in humans and animals. This is paradoxical because the main sugar in most fruits, fructose, is an obesogenic compound. In fact consuming the juice of fruits has been shown to cause rapid reductions in insulin sensitivity, and the obesogenic effects of fruit juice have been shown to be similar in magnitude to those of soft drinks. Therefore the juice of fruits containing fructose is able to cause weight gain, but the whole fruit does not have this effect. This suggests that some component or components of fruit are able to protect the consumer from weight gain. The beneficial effects of fruit are reasonably well established, and these likely relate to the high antioxidant content of most fruits, to the high fibre content, or both. In fact, low fruit consumption is considered to be a major risk factor for cardiovascular disease. Further, studies show that increasing the daily consumption of fruit is associated with weight loss or protection from weight gain.
The evidence that fruit is protective of obesity is consistent between observational studies, animal studies and clinical trials. The anti-obesity effects of fruit are present in animals and humans, suggesting that this is not a phenomenon unique to humans. However, the protective effects of fruit may not be consistent with all fruit. For example, processed fruit including tinned, juiced and dried fruit may not offer the same beneficial effects as whole fruit. Fruit juice is missing most of the dietary fibre associated with fruit, tinned fruit often has additional sugars added for preservation purposes and dried fruit has a low water content that means that overeating the fruit is more likely. In addition, the amount and type of sugars in various fruits can vary. Further, certain fruits such as bananas when unripe have a high starch content, and this starch is slowly converted to sugar, which increases the sweetness of the ripe fruit. Consuming fruit at different stages of ripeness could therefore also affect the obesogenic potential.
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