July 6, 2008

Certain foods have fat-promoting actions, causing changes in hormones and metabolic activities that increase the risk for fat accumulation and obesity; whereas, other foods have fat-fighting actions. Fat-promoting foods, if avoided and replaced with items that reduce the risk for fat accumulation, would help to maximize weight loss success and long-term maintenance post-surgery. Over the next several issues of the Silhouette, the research section will examine foods that promote fat and those that may help to reduce the risk for obesity. The first of this series of articles discusses why processed grains increase the risk for obesity and why, calorie for calorie, processed grains are so much more fattening than whole grains. 

Whole Grains vs. Processed Gains
Do you know the difference between the terms ‘whole grain’ and ‘processed grain’? A whole grain is the seed of the plant and consists of 3 major components. The first of these is the bran or outer layer of the seed, which is high in fiber, vitamins, minerals, and phytonutrients. The center of the seed is the germ and it, too, is high in vitamins, minerals, as well as protein and fat. The third part of the seed is the kernel and consists primarily of carbohydrate. Whole grains, then, contain all the components of the plant seed, along with its high fiber content and nutrients.

Refined or milled grains are those that have had the bran and germ removed through high-heat roller mills. Such processing removes the nutrient and fiber content of the grain, leaving behind the carbohydrate kernel. The advantage to refining or milling is to increase the shelf life of the product. Processed grains vs. whole grains have a much longer shelf life and are resistant to pests, such as rodents who prefer to eat the nutritious parts of the grain. To increase the nutrient value of the processed grains, manufacturers ‘enrich’ or, in other words, add back to the refined grain some but not all of the lost vitamins. Until recently, most grain products in the grocery market were processed or refined including bread and baked goods, cereals, crackers, and rice products. 

Calorie-for-calorie processed grains are more fattening than are whole grains and for several reasons. First, processed grains contain mainly carbohydrate and, when consumed, are rapidly absorbed, resulting in an increase in blood sugar. The rise in blood sugar results in a concomitant increase in the production of insulin, the hormone that regulates sugar in the body. Insulin lowers blood sugar levels by promoting the uptake of sugar into tissues and by stimulating its metabolism or storage. However, insulin can also increase body fat. 

Insulin drives fat into fat (adipose) tissue and increases fat conversion into its storage form, triglyceride.   At the same time, insulin inhibits the breakdown of fat. An increase in fat uptake and a reduction in its breakdown would promote fat accumulation and weight gain.   In addition, insulin enhances the conversion of sugar to fat, making even more fat available for storage in adipose tissue. Thus, foods that cause insulin levels to rise significantly, such as processed grains, are more fattening than those that do not.

Whole grains contain fiber, which can reduce the absorption of sugar and other carbohydrates.   A decrease in the rate of absorption of carbohydrates in the diet would help to prevent the rapid rise in blood sugar and the concomitant increase in insulin. Studies find that high fiber foods reduce blood levels of sugar and insulin, and a decrease in insulin would reduce the risk for fat accumulation. Too, whole grains with their high fiber content decrease the absorption and blood levels of fat, resulting in a decrease in the availability of fat for storage. In these ways, whole grains are calorie-for-calorie less fattening than are processed grains.

Whole grains are also less fattening than processed grains because they reduce appetite. Foods high in fiber take longer to chew and also tend to absorb more water, expanding inside the stomach and causing the person to feel full. Fiber also stimulates the production of certain gut factors that reduce motility (movement of food through the gut), causing the person to feel full longer and eat less frequency. Furthermore, certain of the gut factors increased by fiber in foods signal the appetite centers of the brain to cause the individual to feel satiated (full). 

Finally, whole grains are calorie-for-calorie less fattening than are processed grains because they have far greater nutrient content. The whole grain contains phytonutrients and antioxidants, which reduce or protect against oxidative stress, one of the mechanisms underlying obesity. The whole grain, unlike the processed grain, is also rich in many of the B-complex vitamins that serve as important co-factors in metabolic reactions involving the absorption and utilization of food.   Refined grains may be enriched with certain vitamins but not all of those found naturally in the grain, reducing their nutrient value and interfering with appropriate metabolic activity.

For all of the reasons described above, ‘whole’ grain foods are less fattening and more vitamin replete than are ‘processed’ grains.   It is important, therefore, to recognize which grain foods are ‘processed’ and which ones are ‘whole’.   In this issue of the Silhouette, the ‘Nutrition’ page lists grain foods that are generally ‘whole vs. processed’, how manufacturer’s labeling of grain foods can be deceptive, how you can be assured that the product labeled ‘whole grain’ actually is, and practices that may help you (and your family) replace your favorite ‘processed’ grain foods with ‘whole’ grain alternatives. Changing your diet in such manner as to reduce the consumption of fat-promoting foods, such as processed grains, while increasing your intake of fat-fighting items, including whole grains, will not only reduce your risk for weight gain/regain but also help to optimize your health through improved nutritional status.

By Cynthia Buffington, Ph.D.