A low GI breakfast before exercise could help with weight loss, a study conducted at The University of Nottingham has found.
The benefits of physical activity and a balanced diet are well documented and already form the basis of many public health recommendations. But could the type of food you eat prior to exercise impact on the results of your workout?
A study led by Dr Emma Stevenson in the University’s School of Biomedical Sciences and published in the Journal of Nutrition looked at eight healthy but sedentary young women following an overnight fast. In one study period they were given a breakfast of food known to cause large rises in blood glucose — those with a high glycemic index (GI). In another study period the same women breakfasted on food with a low GI. Both the high GI and low GI breakfasts had a similar calorific value.
The high GI breakfast consisted of cornflakes and milk, white bread and jam and a carbonated glucose drink. The low GI breakfast was made up of muesli and milk, tinned peaches and yoghurt and apple juice. Both breakfasts contained the similar amounts of carbohydrate, fat and protein and contained approximately 265 kcal (based on a 50kg individual).
Three hours later the participants did a 60-minute walk on a treadmill at a speed and gradient equivalent to 50 per cent of their maximum exercise abilities. A lunch — the same in both study periods — was then provided.
Blood samples were taken from the test subjects before they ate breakfast and then repeatedly throughout the three hours after breakfast, and for a two hour post-exercise period. Samples of expired air were also collected from the participants at regular intervals both at rest and during exercise. This provided an estimation of the amount of oxygen being consumed and carbon dioxide being produced by the participants. From this, energy expenditure and the amount of carbohydrate and fat being oxidised was calculated. Appetite was also assessed throughout the experimental protocol using visual analogue scales.
Blood glucose concentrations were higher — as expected — after the high GI breakfast than the low GI breakfast, and had returned to normal levels by the time the subjects started to exercise. But plasma free fatty acids (FFA) — which indicate the amount of fat being used as an energy source — began to rise two hours after the low GI breakfast was consumed. Exercise then led to a rapid increase in FFAs in both groups — but concentrations were higher in the low GI group. After lunch the concentration of FFAs was the same in both groups, but overall fat oxidation was higher in the low GI group than the high GI group.
Dr Stevenson said: “Following the study, we concluded that consuming a low GI breakfast increases fat oxidation both at rest and during subsequent exercise. Longer-term studies are required to investigate whether the combination of a low GI diet and regular exercise will result in an increase in fat mass loss. A low GI breakfast also had an impact on appetite, with test subjects feeling fuller for longer after they’d eaten these types of foods.
“As such, individuals trying to shed fat may consider choosing low GI foods before they exercise.”
Notes to editors: The University of Nottingham is ranked in the UK's Top 10 and the World's Top 100 universities by the Shanghai Jiao Tong (SJTU) and Times Higher (THE) World University Rankings.
More than 90 per cent of research at The University of Nottingham is of international quality, according to RAE 2008, with almost 60 per cent of all research defined as ‘world-leading’ or ‘internationally excellent’. Research Fortnight analysis of RAE 2008 ranks the University 7th in the UK by research power. In 27 subject areas, the University features in the UK Top Ten, with 14 of those in the Top Five.
The University provides innovative and top quality teaching, undertakes world-changing research, and attracts talented staff and students from 150 nations. Described by The Times as Britain's “only truly global university”, it has invested continuously in award-winning campuses in the United Kingdom, China and Malaysia. Twice since 2003 its research and teaching academics have won Nobel Prizes. The University has won the Queen's Award for Enterprise in both 2006 (International Trade) and 2007 (Innovation — School of Pharmacy), and was named ‘Entrepreneurial University of the Year’ at the Times Higher Education Awards 2008.
Nottingham was designated as a Science City in 2005 in recognition of its rich scientific heritage, industrial base and role as a leading research centre. Nottingham has since embarked on a wide range of business, property, knowledge transfer and educational initiatives (www.science-city.co.uk) in order to build on its growing reputation as an international centre of scientific excellence. The University of Nottingham is a partner in Nottingham: the Science City.