The 3rd Obesity Presumption in the New England Journal of Medicine on obesity myths, presumptions and facts paper states that,
“Eating more fruits and vegetables will result in weight loss or lessweight gain, regardless of whether one intentionally makes any other behavioral or environmental changes.”
The notion underlying this presumption is the common belief that,
“By eating more fruits and vegetables, a person presumably spontaneously eats less of other foods, and the resulting reduction in calories is greater than the increase in calories from the fruit and vegetables.”
While this may well be the case for some people, unless those fruits and vegetables are being eaten raw, chances are that they may well be contributing a significant amount of calories to your diet (think Indian vegetarian curry or a vegetable stir-fry).
It is therefore by no means surprising that simply going vegetarian (or even vegan) will do much for your weight even if it may take longer to eat the same amount of calories.
Thus, the studies quoted in this paper failed to find any impact on body weight by simply increasing fruit and vegetable intake without making any other adjustments to your diet – in the end what counts with regard to body weight are calories – irrespective of whether these are derived from vegetables, fruit, fats, oils, carbs, meats, dairy or alcohol.
If anything, this presumption should serve to remind us that eating healthier food is not the same as eating fewer calories.