By: Rick Mendosa
How full did that meal you just ate make you feel? Did it satisfy your hunger, or did it make you feel like you’ll need a snack later?
Now a new tool is available to measure the hunger-fighting power of certain foods and help with blood sugar control.
Studies by Australian researcher Susanne Holt, PhD, MND, and her associates at the University of Sydney have developed one of the most exciting diet concepts ever. Called the “Satiety Index,” Holt’s tool ranks different foods on their ability to satisfy hunger.
Holt drew up the Satiety Index by feeding 240-calorie portions of 38 different foods to volunteers. The foods were served from under a hood to minimize the influence of appearance, and, if possible, they were served at the same temperature and in the same size chunks.
After eating the volunteers were left for two hours to nibble as they liked from a variety of other foods. Their consumption was closely monitored, and every 15 minutes they were questioned about their hunger to see if their subjective impression of satisfaction matched their eating behavior.
Using white bread as the baseline of 100, 38 different foods were ranked. In other words, foods scoring higher than 100 are more satisfying than white bread and those under 100 are less satisfying.
What Really Satisfies?
Holt found that some foods, like croissants, are only half as satisfying as white bread, while boiled potatoes are more than three times as satisfying, easily the most satisfying food tested. But potatoes in a different form – French fries – did not score well. This type of information can have important implications for those wanting to lose weight. (For Holt’s Satiety Index see page 12)
The chemical make-up of a food is one of the factors that determines how it ranks on the index. “Beans and lentils, for example, contain anti-nutrients which delay their absorption so they make you feel full for longer,” says Holt. “Roughly speaking, the more fiber, protein and water a food contains, the longer it will satisfy. But you have to look at each foodstuff individually – and that is why we think our index will be so useful.”
Another thing that makes a food satisfying is its sheer bulk. “You can eat an awful lot of popcorn without taking in a lot of calories,” says Holt. “It may not weigh much, but it makes your stomach feel full just because it takes up so much space. Oranges come out very high on the index for the same reason – but orange juice probably wouldn’t, even though it has the same number of calories.”
It is, in fact, the size and bulk of potatoes that may account for much of its high satiety. Their “portion weight was up to four times greater than the other foods (for the same caloric content),” Holt and her co-authors note in a paper published in the December 1996 issue of the European Journal of Clinical Nutrition.
As a group, fruits ranked at the top with a satiety index 1.7 times more satisfying, on average, than white bread. Carbohydrate-rich foods and protein-rich foods deter nibbling almost as well. Holt warns, however, that there are big differences between the satisfaction values of individual foods within the same group.
“You can’t just say that vegetables are satisfying or that bakery products aren’t, because there can be a two-fold difference between two similar foods,” says Holt. “We found that bananas are much less satisfying than oranges or apples, and that wholemeal bread is half again as satisfying as white bread (157 compared to 100 respectively).”
This too can be valuable information to the weight conscious. “A diet which simply recommends cereal for breakfast overlooks the fact that muesli is only half as satisfying as porridge (oatmeal),” she adds.
In general, the more satisfying a food felt, the more effective it proved as a nibbling deterrent. But even here there were some surprises.
“Fatty foods are not satisfying, even though people expect them to be,” says Holt. “We think the reason is that fat is seen by the body as a fuel which should be used only in emergencies – it stores it in the cells instead of breaking it down for immediate use. Because it doesn’t recognize the fat as energy for immediate use, the body does not tell the brain to cut hunger signals, so we go on wanting more. Carbohydrates are the opposite – they raise blood glucose so the body knows it has gotten enough fuel.”
Jellybeans also scored higher than expected. Volunteers fed jellybeans did not feel satisfied, yet they ate very little afterwards. This resulted in the sweets getting a satiety rating of 118 – higher than that of muesli and yogurt and almost the same as white pasta.
“I suspect the reason that the jellybeans came out so well was that they made our volunteers feel slightly nauseous,” says Holt. “We’ll be doing some research on that one – if we can persuade people to act as volunteers!”
A Few Words of Advice
Holt is concerned that there may be some confusion in the interpretation of her study’s findings. “The Satiety Index scores reflect the total amount of fullness produced by the set portions of the test foods over two hours – i.e., short-term satiety. Although most foods with high Satiety Index scores kept fullness relatively high for the whole two hours, there were a few exceptions,” Holt notes.
“The fruits were served in very large portions, but fullness dropped off quickly towards the end of the second hour, reflecting the rapid rate of gastric emptying (oranges and apples and grapes are mainly sugar and water).”
“Many ‘health-conscious’ dieters,” she continues, “will eat a meal based on several pieces of fruit and some rice cakes (in Australia anyway) and then wonder why they feel ravenous a few hours later. These kinds of extremely low-fat, high-carb meals do not keep hunger at bay because they are not based on slowly-digested carbs and probably don’t contain enough protein. A dieter would be better off eating a wholesome salad sandwich on wholegrain bread with some lean protein like tuna or beef and an apple. This kind of meal can keep hunger at bay for a very long time.”
The Work Continues
Holt now works as a research scientist with the Commonwealth Scientific and Industrial Research Organization (CSIRO), Australia’s largest scientific research agency, and is continuing to develop the Satiety Index.
“We’ve just done a short study comparing the satisfying power of different breakfasts,” she writes of her as-yet-unpublished work. “Two high-fat breakfasts of fried eggs and bacon and toast or croissants and jam were much less filling than two equal-calorie high-carb breakfasts which were either rapidly digested (cornflakes with sugar and toast and jam) or slowly digested (All-Bran with banana slices, toast and margarine),” she adds.
Holt is also interested in how foods affect mood and alertness. “The two high-carb breakfasts tended to improve alertness to a greater extent than the two high-fat breakfasts. Also, because the subjects were not completely satisfied by the two high-fat meals, they tended to be grumpy and a bit more aggressive or disappointed.”
Additional studies of satiety among children are also being planned.
Clearly, future research is warranted and Holt hopes to do it. Eventually tables showing the ratio of satiety to energy will be developed as a tool in planning diets for weight loss or gain. This way we can minimize our hunger pangs and make it easier to stay on our diet programs.
Adapted from an article that originally appeared on the website, http://www.diabetesnet.com. See this website, from John Walsh, PA, CDE, for updates on this research as they become available.