GL Scientific Evidence

“Substantial and consistent scientific evidence of the highest quality shows that a Low GL diet is more effective than conventional low fat or low carb diets, causes more weight loss on the same calories, reduces hunger and sugar cravings, is easy to maintain and good for your health.” Scientific Advisory Board on Weight Management

“Substantial and consistent scientific evidence of the highest quality shows that a Low GL diet is more effective than conventional low fat or low carb diets, causes more weight loss on the same calories, reduces hunger and sugar cravings, is easy to maintain and good for your health.” Scientific Advisory Board on Weight Management

This review documents the evidence that:

    • A Low GL diet is most effective for weight loss – more so than low calorie, low fat diets or high protein, low carb diets


    • A low GL diet causes more weight loss on the same calories – by positively affecting metabolic rate


    • A low GL diet is easy to maintain – by reducing hunger and craving for sweet foods


  • A low GL diet is good for your health – creating rapid improvements in cardiovascular health and blood sugar control, and long-term reduced risk for cardiovascular disease, diabetes, cancer and dementia.

 See the evidence for yourself (last updated 2018)






Obesity is Wide Spread

    • One in two people in Britain are overweight


    • One in five are obese


    • Obesity costs the NHS close to £1 billion


    • Obesity causes 30,000 premature deaths


    • Obesity is responsible for over 20 million working days lost per annum and 40,000 lost years of working life


  • 1,000 people in Britain become obese every day

A brief history of losing weight

Weight loss diets as we know them started with the discovery of calories. The ability to measure the energy inherent in a food as calories led to the equation that one’s weight was the net result of calories consumed from food, less calories expended by exercise/activity and the body’s own metabolic needs, called the metabolic rate. Since fat has more calories per gram (9kcals per gram) than protein or carbohydrate (3.75cals for protein, 4kcals for carb) original weight loss diets were low calorie, low fat diets – examples of which are Rosemary Conley’s, Weight Watchers, and Slimming World. Despite the emphasis on low fat, low calorie diets over the past two decades the percentage of people overweight and obese has steadily risen.

Increasing interest in carbohydrates as a cause of obesity arose from three findings. First, that low blood glucose levels are the primary trigger of hunger and hence eating. Secondly, that only carbohydrate, not protein or fat, has a significant effect on altering blood glucose levels. Thirdly, that the incidence of overweight and obese people in the population has continued to rise despite decreasing calorie and fat intake and increasing exercise.

Government statistics show that the amount of calories we eat has steadily decreased over the last 15 years, while the percentage of obese people has steadily increased.  In addition, the 1998 Health Survey for England estimated that women increased their level of physical activity between 1994 and 1998, from 22 to 25 per cent, for men it seems there has been little change. Conversely, carbohydrate, and more particularly sugar intake, has also risen in line with increasing obesity.

These findings led to a different weight loss strategy involving high protein and low carbohydrate. Examples of which are the Atkins Diet. Such diets have proven, in many cases, slightly more effective than low calorie low fat diets, largely due to reducing appetite by stabilising blood sugar. However, their long-term results are not impressive, often due to poor compliance, a product of unnecessary over-restriction of carbohydrates. Their long-term effect on health is also questionable.

Increasing awareness that not all carbohydrates affect blood sugar in the same way led to the creation of the Glycemic Index of foods. The Glycemic Index or GI of a food is a measure of how quickly the sugars within a food raise blood sugar, and for how long they remain elevated, compared to glucose which is the body’s direct fuel source. This led to diets based on eating more low GI foods and less high GI foods as a means to control appetite and weight.

Why GL is more accurate than GI

Diets based on eating low Glycemic Index (GI) foods have a major problem. They are unquantifiable since the GI of foods only tells you about the quality of the sugars in a food in respect of raising blood sugar levels. The GI score tells you nothing about the quantity of carbohydrate within a food. (For example, both carrots and chocolate contain similar high GI, fast-releasing sugars and therefore share the same GI score. However, carrots contain a fraction of the amount of available carbohydrates compared to chocolate. Hence, you would need to eat a lot more carrots to end up with the same effect on your blood sugar levels.)

By knowing both the quantity of carbohydrates eaten and the GI of the food in question the total Glycemic Load (GL) of a diet can be determined. Low GI diets are therefore only crude indicators of benefit for low Glycemic Load (GL) diets since it is possible to eat low GI foods in abundant quantity, resulting in a high GL diet. GL is therefore a superior, quantifiable and accurate measure of a diet’s effect on blood sugar balance, by taking both the quantity of carbohydrate eaten (the factor taken into account in high protein, low carb diets), and the type of carbohydrate eaten (the factor taken into account in GI diets), which is the primary mechanism responsible for appetite control and hence food consumption.

Scientific Advisory Board on Weight Management

Dr David Haslam, MB BS DGM is a GP and the clinical Chair of the National Obesity Forum, responsible for formulating the guidelines for obesity management in primary care and also in childhood obesity for the Royal College of Paediatrics and Child Health.

Patrick Holford BSc(Hons), DipION, FBant is the founder of the Institute for Optimum Nutrition. He published the first UK book on the effect of low glycemic load diets, the Metabolic Diet, in 1987 and has continued to research the weight and health effects of glycemic load, culminating in the Holford Low GL Diet, published in 2004.

Aliya Dallara, BSc(Hons) Nutrition and Health Sciences, trained in nutrition at Kings College, London and is representative of the Institute for Optimum Nutrition

Deborah Colson DipION, MBant is a nutritional therapist at the Brain Bio Centre in London and researches the effects of glycemic load on mental and physical wellbeing.

Key Scientific References

GL and Mental Health

A prospective study of 70,000 post-menopausal women followed over 3 years finds that the higher the GL of their diet the greater was their risk of suffering from depression. Those in the top fifth of GL versus the bottom fifth were 22% more likely to be depressed. The same was true for those with more added sugars in their diet. Conversely, the more non-juice fruit, vegetables and fibre the lower was the risk. Refined grains also increased risk while wholegrains did not. The researchers recommend that low GL diets be considered for the treatment of post-menopausal depression.

J. Gangwisch et al, American Jounral of Clinical Nutrition, 2015

Support for Weight-loss and Low GL Diet

HOLFORDirect has a range of books and supplements to support weight-loss and the Low-GL Diet lifestyle.