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- Eating fibrous food replaces the high caloric foods
- Chewing may increase satiety
- Bulk of fiber and water increases satiety
- Fiber slows down absorption of nutrients
- Fiber slows down absorption of fat which leads to increase of satiation
- Fiber slows down absorption of carbohydrates which lowers insulin levels
- Fiber reduces inflammation which is linked with obesity and metabolic syndrome
- General studies showing that fiber increases satiety and reduces hunger
Dietary fiber is not a magic solution for weight loss. There is no strong evidence of long term, direct effects of fiber on weight loss and more studies are needed. (1) Studies that show positive effects are mostly observational, while clinical trials fail to proof these effects. However, fiber makes an important contribution to factors related to weight loss/control and overall good health.
Specific fiber action that may contribute to weight loss.
Eating fibrous food replaces the high caloric foods
In comparison to others, higher energy compact forms of food, fiber has a higher volume to calorie ratio. Since the stomach has a limited capacity, the lower energy/higher volume food we eat the less high energy foods will fit. (read more..)
Fiber provides some calories, however only in negligent amounts during the fermentation process in the colon. (2)
Chewing may increase satiety
Fiber in the diet makes us chew more. Chewing makes us eat slower, promotes saliva and gastric juice secretion which results in an increased sensation of being full for longer periods of time. (5, 6, 7)
Bulk of fiber and water increases satiety
Fiber slows down absorption of nutrients
Viscous fibers form a gel like substance that slows down the digestion and absorption process of nutrients, specifically by delaying the release of food from the stomach to the intestine and transit within the small intestine. Viscous fiber mixes with food and digestive enzymes and interacts with the movement of carbohydrates and fats though the surface of mucosa in the intestine. (For more details on fiber types see article Fiber) (2, 4, 8, 7, 9)
Fiber slows down absorption of fat which leads to increase of satiation
Because it slows down fat absorption, there is increased fat in the intestines. The presence of extra fat in the small intestines for a prolonged period intensifies the feeling of satiety. In other words, if the fat is absorbed quickly, the feeling of satiety does not kick in until after we have had too much to eat. (2, 10)
Fiber slows down absorption of carbohydrates which lowers insulin levels
Faster absorption of carbohydrates increases the insulin resistance which may lead to an increase of fat accumulation in fat cells. Fiber slows down carbohydrate absorption, and therefore, lowers the insulin levels in the blood. This is beneficial in improving insulin sensitivity and reduces the risk of accumulating fat in the fat cells. (11, 10)
Fiber reduces inflammation which is linked with obesity and metabolic syndrome
Soluble fiber, also called prebiotic, feeds friendly intestinal bacteria responsible for a healthy intestinal environment. Bacteria digests the fiber producing short-chained fatty acids which in turn are used by colon cells, reducing inflammation and lowering the risk of inflammatory diseases. Chronic inflammation is associated with higher insulin resistance and leptin level (satiety level), resulting in weight gain, metabolic syndrome and obesity. (12, 13)
General studies showing that fiber increases satiety and reduces hunger
There are several studies showing a general association between dietary intake of fiber and weight loss or weight management. The main results of the studies are presented below.
- Dietary and supplementary fiber increases a feeling of satiety and reduces hunger and energy intake. Systematic review of clinical trials show that increasing fiber intake by 14g per day for more than 2 days, decreases the amount of energy consumed by 10% and body loss of 1.9kg in a 3.8 month period.
- By having a higher fiber diet, obese people have been shown to reduce their energy intake by 18% (around 2.4kg of body weight loss) and lean people by 6% (around 0.8kg of body weight loss).
- Currently in the U.S., people consume on average 15g of fiber per day. Recommended levels are 25-30g/day. (14)
- Epidemiological studies show that high fiber diets help in weight management by increased satiety, decreased absorption and altering the secretion of gut hormones. (15)
- A large study of 44 publications of epidemiological studies, which included 107 fiber treatments, showed that 39% of people observed significant reduction of appetite and 22% ate less while on fiber supplementation. The bulk of these studies have revealed that dietary fiber is associated with lower body weight. (16)
- A 2010 prospective cohort study showed that high dietary fiber intake prevents an increase in body weight and waist circumference. (17)
- An intake of 20-27g per day of fiber from whole foods or 20g from supplements shows benefits in weight loss. (18)
- A 2011 systematic review of 61 controlled trials showed that viscous fibers, such as pectins, beta-glucans and guar gum, reduced appetite and overall energy intake more than non-viscous types. Overall, the study found, however, that the energy intake has not decreased significantly and the effects on body weight loss were small. (19)
NUTRITION FACTS VS NUTRITION MYTHS
You will find a summary of the most common nutrition myths and evidence-based nutrition facts here.