If you're like most health-conscious people, you scrutinize the nutritional information on food products before you commit to buying them. Cholesterol, sodium, carbs, proteins, fats and total calories are all run through your mental processor as you evaluate a food to determine its overall worth and its likelihood of adding pounds to the scale. But be it by design or for unavoidable reasons related to disease processes, you may not absorb 100 percent of the calories in your food.
Bulimia Nervosa
Eating disorders are common in the U.S. population among both adolescents and adults, with females representing the majority of those afflicted. Bulimia is one such disorder, and bulimics either intentionally vomit after meals or take laxatives in an effort to lower the percentage of calories absorbed. While determining the fraction of calories "lost" through vomiting is difficult to impossible, Dr. George Bo-Linn found that the use of laxatives decreased calorie absorption by only 12 percent, rendering an already hazardous practice even less useful.
Short Bowel Syndrome
According to the National Digestive Diseases Information Clearinghouse, short bowel syndrome refers to malabsorption of nutrients in people that have had more than half of their small intestine surgically removed, or are missing a similar fraction of the small bowel owing to injury or congenital defect. Affected people require intense nutritional support to sustain life. A study of patients with this condition published in "The Lancet" in February 1994 demonstrated that the ratio of carbohydrates to fats in the diet was a strong determinant of caloric absorption fraction, with a high-carb, low-fat diet yielding an absorption of 69 percent of calories--20 percentage points higher than with a high-fat, low-carb regimen.
Bariatric Surgery
Bariatric surgery, often generically referred to as gastric bypass or "stomach stapling," encompasses a number of related procedures performed on morbidly obese people that have been unable to lose weight by ordinary means and whose health is in grave danger owing to complications from diabetes or other conditions. While some degree of malabsorption may occur in people that have had this surgery, the overwhelming majority weight loss results from a drastically reduced stomach volume. Therefore, the percent of calories absorbed is about the same in bariatric surgery patients as it is in the general population.
Dietary Fiber
The nutritional information on food packaging includes the number of grams of protein, carbohydrate and fat, substances with 4, 4 and 9 calories per gram respectively. Many foods, however, contain dietary fiber, which is included under the carbohydrate heading. As a result, the total number of calories available for absorption in such foods falls short of that implied by the constituent nutrients. For example, a cereal with no fat, 5 g of protein and 30 g of carbohydrate per serving would appear to have 140 calories per serving, but if half of those carbs are in the form of fiber, the number is actually 80 calories and only about 60 percent of this food is absorbed.
References
- "Annals of Internal Medicine"; Purging and Calorie Absorption in Bulimic Patients and Normal Women; G.W. Bo-Linn et al.; July 1983
- "The Lancet"; Colon as a Digestive Organ in Patients with Short Bowel; I. Nordgaard et al.; February 1994
- National Digestive Diseases Information Clearinghouse: Short Bowel Syndrome
- Weight-Control Information Network: Bariatric Surgery for Severe Obesity
- Training Peaks: A Calorie Is Not a Calorie
Member Comments