Cite evidence from the literature on humans and rats that suggests that obesity

The genetic literature suggests that there is a strong heritability factor for obesity and that family environment, which would be expected to transmit eating habits, has a remarkably small effect. Although no simple genetic defect has been found for obesity, it is clear that there are important differences in metabolism that result in some persons easily gaining weight during periods of access to high-energy diet, while others appear to be resistant to gaining weight. The rate of obesity has increased rapidly, faster than could be explained by a genetic mechanism.  Recent studies suggest that the use of high fructose as a sweetener has facilitated weight gain. 

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