Food/Health Heat loss and obesity

Press, 18 December 1982, Page 12

Food/Health Heat loss and obesity

As food is absorbed into the body, heat is generated. It has long been known that the amount of food eaten by different people undertaking about the same amount of work, varies greatly. Some skinny or lean people in particular, appear to be able to eat large amounts of food and never put on weight. In contrast, thrifty genotype families already know that they “run to fat” easily. People from such families merely need to “look at food” and they feel that weight is gained.

It has also been known to nutritionists for a long time that certain foods when eaten will generate more heat.

Such heat, due to what is called the “specific dynamic action of food,” raises the temperature sligthly and thus energy is lost from the body.

As yet unknown changes probably take place in the distribution of blood flow.

The more heat generated, the more use of energy. This fact is well known in that

many thrifty genotype families — or those prone to obesity, find it easier to lose weight when the weather is still cool but- fresh green vegetables arrive — that is, in the spring.

High energy foods

For families and individual people prone to become stocky and run to fat, high energy foods must be avoided.

It has long been recognised that both the longer that eating is prolonged during a meal, and the degree of stomach distension, reduce appetite. So desire for further food is reduced. Foods contain fat or refined carbohydrates should be avoided. Fats containing nine calories of energy for each gram eaten, instead of only four calories provided when each gram of carbohydrate or protein is eaten. Carbohydrates in their natural form, such as wheatgrains, potatoes and yams, rice or raw sugar cane, need to be slowly broken down before they can be absorbed. If, however, the potatoes go through the factory and come out as chips, or if the sugar-cane is processed, less energy and. time is required in the digestive processes. Such processed carbohydrates are rapidly absorbed. This is especially so for sucrose and glucose. Glucose is a simple, six carbon sugar made in factories. When dissolved in water and drunk it is almost instantly absorbed.

Professor

Don Beavon

Sucrose is also a refined sugar processed from cane and beet. It has been widely used in the last 100 years as table sugar. This sugar has two simple units, or monosaccharides, linked together. When the sugar is eaten digestive juices split the disaccharide to its two constituent parts. These two simple sugars are glucose and fructose. A new experimental substance for the treatment of obesity and diabetes is a disaccharidase inhibitor. This blocks the breakdown of surcrose, and. so prevents it being absorbed from the intestines.

Single sugars such as glucose and double sugars, or disaccharides like sucrose, are thus absorbed differently

and more slowly. Is this important?

Sugar absorption

As New Zealanders move from teen-age years into middle life, about a third of the men and about a half of the women become overweight. This is damaging to future health.- Once overweight, heat is lost with more difficulty.

Doctors Nawfal Sharief and lan MacDonald, from Guy’s Hospital Medical School, in London, measured heat production after eating sucrose or glucose in a study. They used measurements such as oxygen usage and carbon dioxide production to give measured increased in metabolic rates.

They confirmed a longheld belief that a more rapidly absorbed carbohydrate, such as glucose, lost less heat than a sugar like sucrose, which needed to be broken down.

In obese subjects these differences were not observed. For New Zealanders living in an energy-rich environment, the lessons are clear cut.

Avoid’ readily obsorbed sugars such as sucrose, or indeed any highly processed carbohydrates. Our high-fat diets give us energy-rich foods. Refined sugars may be the last nutrient staw in a country where thrifty genotpye people are particularly at risk.