High fibre diets are known to have a number of beneficial effects. The benefits of high fibre diets include protection from cardiovascular disease, type 2 diabetes and cancer. Many of the health benefits of fibre actually stem from its ability to cause weight loss. Foods such as legumes and oats may be able to cause weight loss because of their high fibre contents. The obesity epidemic in the developed nations may stem in large part from the low fibre content of the diet.
Types Of Fibre
There are two main types of fibre. Soluble fibre and insoluble fibre. Both fibres are made up of the non-digestible parts of plants, but they differ in their ability to absorb water. While insoluble fibre does have health benefits, it is insoluble fibre that is likely beneficial to weight loss. This is because as it absorbs water, it creates a physical gel-like barrier that prevents the absorption of glucose from the gut. This lowers the glycaemic index of any carbohydrates in the meal.
Glycaemic Effects Of Fibre
Lowering the rate that glucose enters the blood appears to have huge health effects. In particular it may decrease nutrient overload on the liver, which in turn lowers the amount of carbohydrate that is converted to fat. This can improve insulin sensitivity and reduce the risk of leptin resistance. Many health effects are now linked to this beneficial glycaemic effect, which is why recommendations are to eat legumes and oats that are rich sources of fibre.
But Is Fibre Calorie Free?
Fibre is just the non-digestible parts of plants. These plant components are made up of largely cellulose and lignins in cell walls, neither which are able to be broken down by human enzymes. As a result they pass straight through the small intestine undigested. Many people assume this means that fibre contains no calorie content. However this is not true and fibre can contribute significantly to daily energy intake.
Short Chain Fatty Acids
Although humans do not possess the enzymes necessary to digest cellulose and lignin, bacteria do. This is how ruminants (goats and sheep) are able to eat grass and other cellulose based plant material. The bacteria in their stomach and intestine ferment the cellulose and this produces short chain fatty acids such a propionate, butyrate and acetate. These are then absorbed and contribute significantly to the daily energy needs of the animal.
Humans And Short Chain Fatty Acids
Just as with ruminants, humans contain bacteria in their intestines that can ferment fibre. These bacteria produce short chain fatty acids and these are absorbed into the circulation where they contribute to daily energy needs. As well as providing energy, the short chain fatty acids also have beneficial metabolic effects and may lower plasma cholesterol levels. They also supply a slow release form of energy that may increase satiety and improve energy efficiency.
The conversion of fibre to fatty acids in the colon is an important part of human health. Those that believe that weight gain is caused by eating too much, do not understand the nuances of human nutrition that make such a contention illogical. Despite containing energy, and contributing to daily energy needs, the more fibre eaten in the diet the more weight that is lost. This paradox illustrates that human nutrition is far more complex that any energy balance equation in a medical textbook.