Thank you for your email. Glycemic index (GI) and glycemic load (GL) diets have been popular for years and new ones are still popping up these days. Despite their popularity, however, lowering the GI of your food choices without lowering your calorie levels will have little or no effect on your fat loss. It's not that GI does not have it's uses, its just that fat loss is not one of those uses.
The GI was originally developed as tool to help diabetics manage their blood sugar. Thats because some foods, which are high on the glycemic index, cause a rapid rise in blood suagar. Other foods, which are low on the glycemic index, lead to a slower rise in blood sugar. This can be valuable information to have handy for diabetics and those with blood sugar concerns. However, the idea that choosing lower GI foods helps you lose weight is NOT supported by the research - it is merely used as "hook" for diet books. The GI is a tool for helping regulate blood sugar, not increasing fat loss.
It's certainly conceivable that some of the foods that are low on the GI might help reduce appetite or that those foods are simply lower in calories, thereby lowering total calorie intake, but then it wouldnt be the low GI per se that contributed to fat loss, but the lower calories (which is ALWAYS the case, by the way - fat loss is about calories first and foremost).
In the latest research that has been released in the years since the 2003 publication of the first edition of my Burn The Fat ebook, there's little doubt left that the low GI diets do not contribute significantly to improving fat loss. When researchers match two groups at the same calorie level and feed one group a high GI diet and one group a lower GI diet, the weight loss will be virtually identical. Blood sugar response, insulin response, and even blood lipids may show differences, for better or worse, but you will NOT see a difference in body fat.
Since my Burn The Fat program was NOT designed for diabetic issues or clinical blood sugar control issues, (it's for healthy people who simply want to burn fat), that is why I did not include the GI in my food lists or prescribe carbohydrate choices based on GI.
As for glycemic load, (GL), that is slightly more useful because GI tells you about blood sugar response but it doesn't tell you about how many calories are in the food. The GL takes into account both the glycemic index as well as the calorie count. For this reason, some people switched from using GI to the GL. However, in all the new research, even the GL did not make any difference in fat loss, if calories were equal.
There's nothing inherently wrong with following a low GI or low GL diet, and for those with blood sugar issues, it may be important. But for fat loss, it's not as helpful as a food selection tool as some diet authorities and glycemic / glucose / GI diet book authors want you to believe.
If you're the scientifically-minded type, I've compiled the latest research so you can see the evidence for yourself.
No effect of a diet with a reduced glycaemic index on satiety, energy intake and body weight in overweight and obese women. Aston, LM, et al. International Journal of Obesity. January 2008. Vol 32. pp 160-165. Human Nutrition Research, Elsie Widdowson Laboratory, Cambridge, UK
OBJECTIVE: To investigate whether a diet with a reduced glycaemic index (GI)
has effects on appetite, energy intake, body weight and composition in
overweight and obese female subjects. Design: Randomized crossover
intervention study including two consecutive 12-week periods. Lower or
higher GI versions of key carbohydrate-rich foods (breads, breakfast
cereals, rice and pasta/potatoes) were provided to subjects to be
incorporated into habitual diets in ad libitum quantities. Foods intended as
equivalents to each other were balanced in macronutrient
composition, fibre content and energy density.
SUBJECTS: Nineteen overweight and obese women, weight-stable, with moderate
hyperinsulinaemia (age: 34-65 years, body mass index: 25-47 kgm2, fasting
insulin: 49-156 pmol l1). Measurements: Dietary intake, body weight and
composition after each 12-week intervention. Subjectively rated appetite and
short-term ad libitum energy intake at a snack and lunch meal following
fixed lower and higher GI test breakfasts (GI 52 vs 64) in a laboratory
RESULTS: Free-living diets differed in GI by 8.4 units (55.5 vs 63.9), with
key foods providing 48% of carbohydrate intake during both periods. There
were no differences in energy intake, body weight or body composition
between treatments. On laboratory investigation days, there were no
differences in subjective ratings of hunger or fullness, or in energy intake
at the snack or lunch meal.
CONCLUSION: This study provides no evidence to support an effect of a
reduced GI diet on satiety, energy intake or body weight in overweight/obese
women. Claims that the GI of the diet per se may have specific effects on
body weight may therefore be misleading.
Glycaemic index effects on fuel partitioning in humans. Obes Rev. 2006
May;7(2):219-26.Diaz EO, et al. Laboratory of Energy
Metabolism and Stable Isotopes, Institute of Nutrition and Food Technology
(INTA), University of Chile, Ave. El Libano 5524, Macul, Santiago, Chile.
The purpose of this review was to examine the role of glycaemic index in
fuel partitioning and body composition with emphasis on fat
oxidation/storage in humans. This relationship is based on the hypothesis
postulating that a higher serum glucose and insulin response induced by
high-glycaemic carbohydrates promotes lower fat oxidation and higher fat
storage in comparison with low-glycaemic carbohydrates. Thus, high-glycaemic
index meals could contribute to the maintenance of excess weight in obese
individuals and/or predispose obesity-prone subjects to weight gain. Several
studies comparing the effects of meals with contrasting glycaemic
carbohydrates for hours, days or weeks have failed to demonstrate any
differential effect on fuel partitioning when either substrate oxidation or
body composition measurements were performed. Apparently, the glycaemic
index-induced serum insulin differences are not sufficient in magnitude
and/or duration to modify fuel oxidation.
No difference in body weight decrease between a low-glycemic-index and a
high-glycemic-index diet but reduced LDL cholesterol after 10-wk ad libitum
intake of the low-glycemic-index diet. Sloth B, et al. Department of Human
Nutrition, Centre for Advanced Food Studies, The Royal Veterinary and
Agricultural University, 30 Rolighedsvej, DK-1958 Frederiksberg C, Denmark.
BACKGROUND: The role of glycemic index (GI) in appetite and body-weight
regulation is still not clear.
OBJECTIVE: The objective of the study was to
investigate the long-term effects of a low-fat, high-carbohydrate diet with
either low glycemic index (LGI) or high glycemic index (HGI) on ad libitum
energy intake, body weight, and composition, as well as on risk factors for
type 2 diabetes and ischemic heart disease in overweight healthy subjects.
DESIGN: The study was a 10-wk parallel, randomized, intervention trial with
2 matched groups. The LGI or HGI test foods, given as replacements for the
subjects' usual carbohydrate-rich foods, were equal in total energy, energy
density, dietary fiber, and macronutrient composition. Subjects were 45 (LGI
diet: n = 23; HGI diet: n = 22) healthy overweight [body mass index (in
kg/m(2)): 27.6 +/- 0.2] women aged 20-40 y.
RESULTS: Energy intake, mean
(+/- SEM) body weight (LGI diet: -1.9 +/- 0.5 kg; HGI diet: -1.3 +/- 0.3
kg), and fat mass (LGI diet: -1.0 +/- 0.4 kg; HGI diet: -0.4 +/- 0.3 kg)
decreased over time, but the differences between groups were not
significant. No significant differences were observed between groups in
fasting serum insulin, homeostasis model assessment for relative insulin
resistance, homeostasis model assessment for beta cell function,
triacylglycerol, nonesterified fatty acids, or HDL cholesterol. However, a
10% decrease in LDL cholesterol (P < 0.05) and a tendency to a larger
decrease in total cholesterol (P = 0.06) were observed with consumption of
the LGI diet as compared with the HGI diet.
CONCLUSIONS: This study does not
support the contention that low-fat LGI diets are more beneficial than HGI
diets with regard to appetite or body-weight regulation as evaluated over 10
wk. However, it confirms previous findings of a beneficial effect of LGI
diets on risk factors for ischemic heart disease.
Should obese patients be counselled to follow a low-glycaemic index diet? No. Raben A. Obes Rev. 2002 Nov;3(4):245-56. Research Department of Human Nutrition, Centre for Advanced Food Studies, The Royal Veterinary and
Agricultural University, Frederiksberg, Denmark.
In diabetes research the glycaemic index (GI) of carbohydrates has long been
recognized and a low GI is recommended. The same is now often the case in
lipid research. Recently, a new debate has arisen around whether a low-GI
diet should also be advocated for appetite- and long-term body weight
control. A systematic review was performed of published human intervention
studies comparing the effects of high- and low-GI foods or diets on
appetite, food intake, energy expenditure and body weight. In a total of 31
short-term studies (< 1 d), low-GI foods were associated with greater
satiety or reduced hunger in 15 studies, whereas reduced satiety or no
differences were seen in 16 other studies. Low-GI foods reduced ad libitum
food intake in seven studies, but not in eight other studies. In 20
longer-term studies (< 6 months), a weight loss on a low-GI diet was seen in
four and on a high-GI diet in two, with no difference recorded in 14. The
average weight loss was 1.5 kg on a low-GI diet and 1.6 kg on a high-GI
diet. To conclude, there is no evidence at present that low-GI foods are
superior to high-GI foods in regard to long-term body weight control.
However, the ideal long-term study where ad libitum intake and fluctuations
in body weight are permitted
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. 2005 Oct;135(10):2387-91. Raatz SK, et al. General
Clinical Research Center, Department of Medicine, School of Public Health,
University of Minnesota, Minneapolis, MN, USA
Reducing the dietary glycemic load and the glycemic index was proposed as a
novel approach to weight reduction. A parallel-design, randomized 12-wk
controlled feeding trial with a 24-wk follow-up phase was conducted to test
the hypothesis that a hypocaloric diet designed to reduce the glycemic load
and the glycemic index would result in greater sustained weight loss than
other hypocaloric diets. Obese subjects (n = 29) were randomly assigned to 1
of 3 diets providing 3138 kJ less than estimated energy needs: high glycemic
index (HGI), low glycemic index (LGI), or high fat (HF). For the first 12
wk, all food was provided to subjects (feeding phase). Subjects (n = 22)
were instructed to follow the assigned diet for 24 additional weeks
(free-living phase). Total body weight was obtained and body composition was
assessed by skinfold measurements. Insulin sensitivity was assessed by the
homeostasis model (HOMA). At 12 wk, weight changes from baseline were
significant in all groups but not different among groups (-9.3 +/- 1.3 kg
for the HGI diet, -9.9 +/- 1.4 kg for the LGI diet, and -8.4 +/- 1.5 kg for
the HF diet). All groups improved in insulin sensitivity at the end of the
feeding phase of the study. During the free-living phase, all groups
maintained their initial weight loss and their improved insulin sensitivity.
Weight loss and improved insulin sensitivity scores were independent of diet
composition. In summary, lowering the glycemic load and glycemic index of
weight reduction diets does not provide any added benefit to energy
restriction in promoting weight loss in obese subjects.
Tom Venuto is a lifetime natural (steroid-free) bodybuilder, independent nutrition researcher, freelance writer and author of the #1 best selling diet e-book, Burn The Fat, Feed The Muscle and the #1 Amazon best-seller, The Body Fat Solution (Avery/Penguin books). Tom has written hundreds of articles and has been featured in IRONMAN, Australian IRONMAN, Natural Bodybuilding, Muscular Development, Exercise for Men, Men's Fitness, Menís Exercise as well as on hundreds of websites worldwide. Tom is also the founder and CEO of the Internet's premier fat loss support community, the: Burn The Fat Inner Circle. To get notified of updates to TomVenuto.Com, subscribe to the free newsletter at: www.TomVenuto.com/free_newsletter.