Thursday, 30 July 2015

Science: When is a Calorie not a Calorie: when it is a high glycaemic index calorie!

Time for some science on When is a Calorie not a Calorie?!

Many sources state ‘‘a calorie is a calorie’’ and there is a lot of truth in that as weight loss is based around fewer calories in than expended (thermodynamic law). However some foods are rapidly absorbed giving a quick energy hit that can be useful around intense exercise (eg cyclists energy gels) but generally it not great for feeling full (satiety). Hence glycaemic index or GI. 
high-GI meals produce larger glycaemic and insulinaemic responses...a rapid peak and then rapid trough. 

The Glycaemic index is a system of ranking the glycaemic potential of the carbohydrates in different foods. It was first proposed as an alternative means of classifying carbohydrate-containing foods in 1981 and some organizations like the American Diabetes Association recognized that the use of the GI 'can provide an additional benefit over that observed when total carbohydrate is considered alone.  Some studies show that high quality foods (but similar calories) enhance weight loss although the effect is not massive

Read a really nice scientific paper on this here:
Esfahani A1, Wong JM, Mirrahimi A, Villa CR, Kendall CW. The application of the glycemic index and glycemic load in weight loss: A review of the clinical evidence. IUBMB Life. 2011 Jan;63(1):7-13. doi: 10.1002/iub.418.

In other studies a diet high in vegetable proteins and oils resulted in greater improvements in CHD risk factors (eg serum lipids and blood pressure, despite similar weight reduction in the conventional low-fat control diet) read about that here  

Jenkins, D. J., Wong, J. M., Kendall, C. W., Esfahani, A., Ng, V. W., Leong, T. C., Faulkner, D. A., Vidgen, E., Greaves, K. A., Paul, G., and Singer, W. (2009) The effect of a plant-based low-carbohydrate (‘‘Eco-Atkins’’) diet on body weight and blood lipid concentrations in hyperlipidemic subjects. Arch. Intern. Med. 169, 1046–1054.

However just because it is low GI, doesn’t mean its high quality. Strict low CHO diets are low GI (and glycaemic load) because of the restriction in carbs but this may be hard to maintain in the long term. Of course diets that deliver adequate nutrition reduce the desire to eat and impact satiety. Low GI/GL diets  replete with fruits, vegetables, and whole grains are rich in nutrients and low in calories and have a higher volume per calorie and offer dietary fiber, resistant starch, and slowly available carbohydrate , all of which have been shown to offer satiation and are associated with reduced body weight. 

How about intervention studies where people are put on a low GI diet? In some but not all studies a low GI diet seems to work. Ebbeling et al.61 showed that an reduced-GL diet was more effective over 12 months at reducing both BMI and body fat in obese adolescents than a conventional energy restricted, low-fat diet. 

Ebbeling CB, Leidig MM, Sinclair KB, Hangen JP, Ludwig DS. A reduced-glycemic load diet in the treatment of adolescent obesity. Arch Pediatr Adolesc Med 2003; 157: 773–779.

A study by Bahadori in Austrian obese adults advised to follow a high carbohydrate, low-GI diet for 24 weeks, reported significant reductions in body fat and unusually small losses in lean mass, with good adherence to the diet

Bahadori B, Yazdani-Biuki B, Krippl P, Brath H, Uitz E, EWascher T. Low-fat, high-carbohydrate (low-glycaemic index) diet induces weight loss and preserves lean body mass in obese healthy subjects: results of a 24-week study. Diabetes, Obesity and Metabolism 2004; 7: 290–293.

A really good review is availabe for free here:

J McMillan-Price1 and J Brand-Miller1 Low-glycaemic index diets and body weight regulation International Journal of Obesity (2006) 30, S40–S46. doi:10.1038/sj.ijo.0803491

500kcal of fruit is not quite the same as 500kcal of ice cream. Theoretically there should be little difference in terms of weight gain/loss, but ice cream will make you crave more as the glucose trough hits that little bit harder and stimulates lipolysis, gluconeogenesis and hunger hormones. High GI foods will also stimulate your brain to want more! The end result is try and eat healthy not just calorie count.



  1. Is there a correlation with natural verses processed GI's?

  2. Hi Richard as you know natural foods tend to have low GI and processed foods high GI. Highly processed foods links with lots of bad outcomes incl metabolic syndrome, diabetes, heart disease, stroke and mortality. Hence the paleo diet. Of course the occassional processed meal is probably ok.