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Question: Does a low glycemic index diet contribute to weight loss?
Answer: The quick answer to this question is "No." Successful weight loss requires a reduced energy diet and an increase in physical activity. Nevertheless, diet books continue to suggest that high glycemic index (GI) foods trigger high insulin levels that in turn cause low blood glucose that spurs new cravings for food.1
To investigate the diet books' claims, the definition of GI first must be clarified. The GI refers to the area under the 2-hour glucose curve following consumption of 50 g of digestible carbohydrate. It does not measure how rapidly blood glucose levels increase; when figures are available, you see the peak glucose response from foods or meals occurring at approximately the same times, although the peak responses may show a modest difference. Insulin responses from low versus high GI meals, when reported, are parallel.2 Researchers don't know if, long term, the GI of a diet can be changed. It appears that most people already eat a diet in the moderate GI range.3–6 In a 12-month study that implemented a low GI diet versus a usual GI diet, there were no differences in mean GI at the study's end.7
In the first published debate on the use of GI diets for weight loss, in 2002, one researcher advised against counseling obese patients to follow a low GI diet based on a review of 20 studies (all <6 months in duration).8 The review found weight loss on a low GI diet in four studies—and on a high GI diet in two studies—with no differences in 14 studies. The average weight loss was 1.5 kg (3.3 lb) on the low GI diet and 1.6 kg (3.5 lb) on the high GI diet. Another research team differed with those findings, concluding from epidemiological evidence and a weight-loss study in obese adolescents that GI does play a role in weight loss and satiety.9 Interestingly, in two subsequent weight-loss trials in obese young adults, no difference in body weight decreases were found when implementing a low GI diet compared with other weight-loss diets.10,11
Low GI and high GI diets for weight loss in adults have been compared in randomized clinical trials. In one 10-week study, no significant difference in weight loss occurred between the high and low GI groups.12 Another study compared three diets (high GI, low GI, and high fat), all with calorie levels 500 kcal less than each subject's estimated energy needs.13 At 12 weeks, changes in weight loss and improved insulin sensitivity were significant in all groups, but no differences between and among the groups were found. All groups maintained their weight loss and improved insulin sensitivity independent of diet composition.
More recently, an eloquently designed 1-year trial compared the effects of
two energy-restricted diets differing in
GI.14 All food for
the two diets (40% carbohydrate from low GI foods compared with 60% energy
intake from high GI foods) was provided to the subjects for the first 6
months. During the next 24 weeks subjects took responsibility for food
preparation and continued their assigned diet. Both groups attended weekly
behavioral support sessions. No significant differences between groups were
found in weight or body fat loss, mean energy intake, hunger, satiety, and
metabolic rate for 
12 months. The investigators concluded that their
findings provide more rigorous support that wide variability in the balance of
dietary macronutrients and glycemic GI has little effect on long-term weight
loss during calorie restriction. They noted a tendency for weight and body fat
regain in the low GI group, which suggests "that reduced energy intake
may be somewhat harder to sustain with low GI regimens long
term."14
Finally, it should be noted that the GI is not necessarily the best indicator of healthy food choices. Soft drinks, candy bars, and premium ice creams have low to moderate GIs. The GI of foods can be lowered by adding fat or adding or substituting sugars, especially fructose and sugar alcohols. Even University of Toronto nutrition professor Thomas Wolever, MD, PhD, one of the originators of the GI concept, has noted, "Whole-wheat bread, brown rice, and brown spaghetti all have the same GI values as their `refined' white versions."15
The bottom line is that calories count! Energy restriction and an increase
in energy expenditure should continue to be the focus of weight loss and
maintenance intervention efforts. Health professionals and the public know
this, but they still want an easier answer. 
Footnotes
|
References
2. Crapo PA, Reaven G, Olefsky J: Plasma glucose and insulin responses to orally administered simple and complex carbohydrates.Diabetes 25:741–747, 1976.[Medline]
3. Rizkalla SW, Taghrid L, Laromiguiere M, et al.: Improved glucose
control, whole-body glucose utilization, and lipid profile on a low-glycemic
index diet in type 2 diabetic men. Diabetes Care 27: 1866–1872, 2004.
4. Salmeron J, Manson JE, Stampfer MJ, et al.: Dietary fiber, glycemic load, and risk of non-insulin-dependent diabetes mellitus in women.JAMA 277:472–477, 1997.[Abstract]
5. Salmeron J, Ascherio A, Rimm EB, et al.: Dietary fiber, glycemic load, and risk of NIDDM in men. Diabetes Care 20: 545–550, 1997.[Abstract]
6. Liese A, Schulz M, Fang F, et al.: Dietary glycemic index, glycemic
load, carbohydrate and fiber intake and measures of insulin sensitivity,
secretion, and adiposity in the Insulin Resistance and Atherosclerosis Study.Diabetes Care
28:2832–2838, 2005.
7. Gilbertson HR, Brand-Miller JC, Thorburn AW: The effect of flexible
low glycemic index dietary advice versus measured carbohydrate exchange diets
on glycemic control in children with type 1 diabetes. Diabetes
Care 24:1137–1143, 2001.
8. Raben A: Should obese patients be counseled to follow a low-glycaemic index diet? No. Obes Rev 3: 245–256, 2002.[Medline]
9. Pawlak DB, Ebbeling CB, Ludwig DS: Should obese patients be counseled to follow a low-glycaemic index diet? Yes. Obes Rev 3: 235–244, 2002.[Medline]
10. Ebbeling CB, Leidig MM, Sinclair KB, et al.: Effects of an ad
libitum low-glycemic load diet on cardiovascular disease risk factors in obese
young adults. Am J Clin Nutr 81:976–982, 2005.
11. Ebbeling CB, Leidig MM, Feldman HA: Effects of a low-glycemic load
vs. low-fat diet in obese young adults: A randomized trial.JAMA
297:2092–2102, 2007.
12. Sloth B, Krog-Mikkelsen I, Flint A, et al.: No difference in body
weight decrease between a low-glycemic index diet and high-glycemic index diet
but reduced LDL cholesterol after a 10-wk ad libitum intake of the
low-glycemic-index diet. Am J Clin Nutr 80: 337–347, 2004.
13. Raatz SK, Torkelson CJ, Redmon JB, et al.: Reduced glycemic index
and glycemic load diets do not increase the effects of energy restriction on
weight loss and insulin sensitivity in obese men and women. J
Nutr 135:2387–2391, 2005.
14. Das SK, Gilhooly CH, Golden JK, et al.: Long-term effects of 2
energy-restricted diets differing in glycemic load on dietary adherence, body
composition, and metabolism in CALERIE: A 1-y randomized controlled trial.Am J Clin Nutr
85:1103–1111, 2007.
15. Wolever TMS: Physiological mechanisms and observed health impacts related to the glycaemic index: Some observations. Int J Obes 30: S72–S78, 2006.
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