Research Update

Should fruit juice be a part of your weight loss plan?

The Study

In this randomized crossover trial, 34 subjects consumed a 400 calorie preload that was either whole fruit or fruit juice. Immediately after consuming the preload, subjects were then presented with a lunch of macaroni and cheese and allowed to eat as much as they wanted. Energy intake and satiety were measured by visual analogue scale. The results were fascinating: 1) Overweight/obese subjects were significantly more hungry after the fruit juice than the solid fruit preload. 2) Subjects consumed significantly less of the macaroni and cheese lunch after ingestion of the solid fruit. 3) Total daily energy intake was significantly higher when obese participants consumed the fruit juice when compared to the solid fruit preload. International Journal of Obesity 2013; 37:1109-14

Take Home Message

Avoid fruit juice if weight loss is your goal and instead focus on whole fruit in its natural form. When you juice a fruit, you concentrate the sugar and eliminate the fiber. This process turns a food that is easy on the blood sugar to one that will cause a rapid spike in blood sugar and then a reactive hypoglycemia that will leave you feeling hungry. In this study, this effect was even more pronounced in those that were overweight or obese.

How does exercise influence hunger?

The Study

15 lean and healthy young men completed two 60 minute trials on separate occasions. Trial #1 was a treadmill run of 60 minutes at 70% of maximum aerobic capacity. Trial #2 consisted of 60 minutes of rest. After each trial, the men were shown images of high and low calorie foods while an MRI of brain activity was taken. Hunger was measured by visual analogue scale and appetite hormones were measured in the blood. The exercise session significantly decreased hunger. The exercise session significantly increased responses in reward related regions of the brain when shown images of low calorie foods and this activation was suppressed when shown images of high calorie food. Levels of ghrelin, a hormone that increases appetite, were significantly reduced after the exercise session. American Journal of Clinical Nutrition 2014; 99:258-67.

Take Home Message

For years, I have noticed anecdotally, that when a new client initiates an exercise program, their diet seems to immediately improve. I thought this was psychological, but it may just be physiological. Although more research is needed in this area, it seems that acutely after exercise, we are less interested in unhealthy food and more interested in healthy food. Consider this just one more reason to include exercise in your weight loss program.