Dietary Preload Positively Effects Weight Loss

A recent study was conducted to evaluate the effects of three different varieties of “preload,” or food eaten before a meal, on energy balance, weight loss, body composition and cardiometabolic risk in obese adults. The results indicated that a dietary preload that was less energy-rich was highly effective in facilitating weight loss among obese adults. Other factors affecting cardiometabolic risks were also seen to improve with addition of preloads. However, the form of the preload–solid, liquid or water–did not have an effect on weight loss.

Obesity is considered to be a risk factor for diabetes and various cardiovascular diseases. Interventions in the form of calorie restriction and reduced energy content in diet have shown positive outcomes in promoting weight control. The results of earlier studies were even more significant when a “preload” was employed. The researchers designed a study to evaluate the effect of grapefruit (solid), grapefruit juice (liquid) and just water preloads, matched by weight, calories, water content and energy density on energy balance, weight loss, body composition and cardiometabolic risk in obese adults.

* Adults (21 to 50 years old) with BMI of 30 to 39.9 and body weight below 300 lbs. were included for the study and instructed to adhere to their normal diet for an initial period.
* In the next phase called Calorie Restriction they were to follow a diet plan with a 12.5 percent calorie restriction for two weeks. No dietary supplements, grapefruit or grapefruit juice were consumed during this period. The subjects maintained records of their diet and activities.
* In the next phase (Calorie Restriction and Preload), after clinical and biochemical tests, the subjects were randomly assigned to one of the three different types of preload (grapefruit, grapefruit juice or water) before each meal for 12 weeks. The portions (of grapefruit and juice) were matched for different parameters like weight, vitamin C etc.
* Clinical and biochemical tests were done after completion of the 12-week period.

Key findings
* Considerable increase in the rate of weight loss (more than 13 percent) was observed when a preload was added before each meal, along with restricting calorie intake. There was no difference in rate of weight loss with the different forms of preload intake.
* Energy density of food and total intake of energy decreased with addition of preloads, irrespective of their form.
* Level of HDL cholesterol (good cholesterol) increased by 6.2 percent with grapefruit preload and by 8.2 percent with grapefruit juice preload. In contrast, HDL cholesterol decreased by 3.7 percent when the preload consisted of only water.
* Even though the overall weight loss due to preloads was the same across the groups (7.1 percent), it indicated lowered risk for metabolic syndromes, such as diabetes.

It was not possible to blind the subjects with respect to the different preload forms; therefore “inclusion bias” could have had an effect on the overall outcome among the different preload groups. Besides, although water preload was an appropriate inactive control, it may have had metabolic effects under certain conditions. Another possibility, though small, is that the overweight adults might have underreported their dietary intakes.

The study demonstrated that weight loss can be achieved in a significant fashion, without decreasing the total amount of food consumed by consuming preloads of less energy content before each meal, and “without inducing the hunger and dissatisfaction often associated with restrictive diets.” The study has also shown that similar results can be achieved, regardless of the form of preload. The active components in certain preloads, like bioflavonoid content in grapefruit juice, may confer additional benefits in the form of reducing cardiovascular disease risk factors. However, additional research is required to further investigate the mechanisms involved in the energy balance and fat breakdown for production of energy.

For More Information:
Effects of Grapefruit, Grapefruit Juice and Water Preloads on Energy Balance, Weight loss, Body composition and Cardiometabolic Risk in Obese Adults
Publication Journal: Nutrition & Metabolism, February 2011
By Heidi J. Silver, PhD; Mary S. Dietrich, PhD; Department of Medicine, Vanderbilt University, Nashville, Tennessee; Department of Biostatistics, Vanderbilt University, Nashville, Tennessee

*FYI Living Lab Reports Are Summaries of the Original Research.
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