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Dr Alex Johnstone

Research Interests

Awareness of the obesity epidemic in Scotland and the associated co-morbidities of type II diabetes and cardiovascular disorders has focused attention on developing novel effective strategies to reduce caloric intake to achieve weight loss. Hunger is one of the main reasons why people fail to lose weight. Diet composition strongly affects energy intake, with human studies highlighting protein as a more satiating macronutrient than either carbohydrate or fat.??

Recently, there has been considerable public interest in the use of high protein-low carbohydrate, ketogenic weight loss diets. Recent work has examined the possible physiological (e.g. protein induced satiety) and psychological (e.g. rapid weight loss) reasons why this regime is popular. We have observed a reduction in ad libitum intake with subjects fed both high-protein-moderate-carbohydrate and high-protein-low-carbohydrate diets. Such evidence suggests that high protein diets could be a key to successful dieting ? being able to eat as much as you want (ad libitum) without feeling hungry and yet lose weight.

There has been recent interest in manipulating sources of dietary protein and assessing the impact on hunger and appetite. Understanding the role of different high protein diets, meals and food products in feeding behaviour is another challenge. Humans eat and overconsume energy for a variety of reasons, often not related to hunger. For example, reward aspects of food, emotional and cognitive factors all play important roles in regulating feeding behaviour. Energy homeostasis is controlled by long-term adiposity signals and short-term gastrointestinal signals. Hedonic factors may over-ride these signals, at least in the short term. The use of functional MRIand PET scan technology is giving new insights as to how feeding is regulated and will surely be a useful tool, in time, to elucidate the role of specific nutrients, including high protein diets, on control of appetite.

References

Recent publications: Alex Johnstone

 Johnstone, A.M. High-protein diets for appetite control and weight loss - the 'holy grail' of dieting? British Journal of Nutrition, 101 (12) June 2009 pp. 1729-1730

Gratz, S., Duncan, S.H., Richardson, A.J., Johnstone, A.M., Lobley, G.E., Flint, H.J., Wallace, R.J. High Protein Diets Impact on Microbial Metabolites and Toxicity in the Human Large Intestine. Microbial Ecology, 57 (3) April 2009 pp. 572-573.

Johnstone AM, Horgan GW, Murison SD, Bremner DM, Lobley GE. Effects of a high-protein ketogenic diet on hunger, appetite, and weight loss in obese men feeding ad libitum. Am J Clin Nutr. 2008 Jan;87(1):44-55.

Whybrow, S., Hughes, D.A., Ritz, P., Johnstone, A.M., Horgan, G.W., King, N., Blundell, J.E., Stubbs, R.J. The effect of an incremental increase in exercise on appetite, eating behaviour and energy balance in lean men and women feeding ad libitum. British Journal of Nutrition, 100 (5), November 2008 pp. 1109-1115

Duncan SH, Lobley GE, Holtrop G, Ince J, Johnstone AM, Louis P and Flint HJ. Human colonic microbiota associated with diet, obesity and weight loss. International Journal of Obesity, ?2008, 32, 1720-1724.

Speakman, J.R., Rance, K.A., Johnstone, A.M. Polymorphisms of the FTO Gene Are Associated With Variation in Energy Intake, but not Energy Expenditure. Obesity, 16 (8) August 2008. pp. 1961-1965.

Johnstone, A.M. Stewart, A.D., Benson P., Kalafati, M., Rechtenwald, L., Horgan, G.W. Assessment of body image in obesity using a digital morphing technique. Journal of Human Nutrition and Dietetics, 21 (3), June 2008 pp. 256-267

Johnstone, A.M., (2007) High protein diets: fact and fiction. Annals of Nutrition and Metabolism 51 (Suppl. 1) September pp. 6-7

Johnstone A.M. Fasting - the ultimate diet ? Obesity Reviews 2007, 8, 211-222.

Duncan SH, Belenguer A, Holtrop G, Johnstone AM, Flint HJ, Lobley GE. Reduced dietary intake of carbohydrate by obese subjects, undergoing weight loss, results in decreased butyrate and the populations of butyrate-producing bacteria in faeces. Applied and Environmental Microbiology 2007, 73(4), 1073-1078.