Photo: Charles Masters

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Avocados: Middle Whittler
It may sound counterintuitive, but slimming down by eating fat—there's nearly 30 grams in an avocado—is an idea that's steadily gaining traction. A small study in Nutrition Journal revealed that overweight people who included half an avocado in their midday meal reported greater satiety three hours later. Researchers also noted that avocado reduced spikes of insulin—a hormone that can promote fat storage, possibly making it harder for you to lose weight.