Rising levels of obesity in developed countries like New Zealand are having a significant effect on the health of the population.
The 2006/07 New Zealand Health Survey found that:
- 1 in 3 adults was overweight (36.3%) and 1 in 4 obese (26.5%).
- 1 in 5 children aged 2–14 years was overweight (20.9%) and 1 in 12 was obese (8.3%).
Despite the introduction of healthy eating programmes, the availability of low-calorie foods and the widely disseminated message to adopt a healthy lifestyle, obesity continues to be a major health concern.
Investigation of a novel solution
Most of the treatments for obesity target energy intake and expenditure, and include dieting and physical exercise, surgery, drugs and many scientifically undocumented remedies. Most of these treatments are not very effective.
A new and emerging approach is to design foods that influence the body’s control mechanisms on appetite and energy intake.
Scientists from Plant & Food Research, such as Dr John Ingram, are currently investigating the ability of plant food components, such as polyphenols, to trick the intestinal sensing system into signalling to the brain a sense of fullness (satiation) and lack of appetite (satiety).
Three main mechanisms that influence satiation and satiety are being targeted.
Nature of science
Science projects such as this involve collaboration between many scientists from different disciplines both within New Zealand and overseas. Along with John, an endocrinologist, chemist Dr Kevin Sutton heads the project, while the team is made up of researchers from different science disciplines including systems biologists, nutritionists, gastric physiologists, microbiologists, food chemists and food industry representatives.
The first involves the chemosensory cells that line the first part of the small intestine known as the duodenum. When stimulated, these cells produce a hormone called cholecystokinin (CCK), which has a positive effect on the satiety centres in the brain. Some of the polyphenolic compounds found in plant foods are being investigated for their ability to cause this hormonal response.
The second mechanism – the ileal brake – involves the release of hormones such as GLP-1 and PYY from the cells lining the last part of the small intestine called the ileum.These hormones also have a positive effect on the satiety centres in the brain. In order to activate this mechanism, the digestion of carbohydrate further up the small intestine has to be delayed so that the ileum ‘sees’ the undigested material and responds by activating the release of satiety hormones. The research centres on finding suitable plant foods or food components that stimulate the ileal brake into action.
The final mechanism targets the bacteria present in the large intestine (colonic effect). These bacteria ferment some of the indigestible carbohydrate present in plant foods, producing short-chain fatty acids.
Certain types of carbohydrate have been found to give a greater production of a short-chain fatty acid called butyrate. Beyond a certain threshold concentration, this acid stimulates the release of hormones that have a positive effect on the satiety centres in the brain.
Research is directed at trying to promote the growth of bacterial populations in the colon that enhance the level of butyrate production following a meal. In addition, plant fibre composition is being looked at, as well as some of the phytochemicals present in certain types of plant foods.
These different mechanisms occur at different times after the consumption of a meal. The CCK response is quite rapid, occurring within 20 minutes or so after consumption of a meal and lasting about one 1 hour.
The ileal brake takes about 1–2 hours and the colonic system is long term – the next meal or even the next day if an enhanced satiety effect has been initiated.
Perhaps a future outcome of Plant & Food Research’s gut hormone work will be specific plant foods or plant food extracts that, on consumption, can assist in the control of energy balance within the body.