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Healthy weight management for many is extremely difficult with most diets failing in the long run. Investigations aimed at enhancing satiety and weight loss have found protein to be effective in humans, but the effects of fibre remain unclear.
In our animal studies and recent human studies, added dietary fibre has been shown to result in elevated gut derived satiety hormone signals. This can lead to reduced energy intake and weight loss. However, other studies have seen elevated satiety signals without associated weight loss.
We are interested in why this happens and are currently investigating whether associated weight loss is dependent on specific bacteria being present in the gut that can use the fibre to produce compounds, such as short chain fatty acids that stimulate the weight loss.
In our earlier studies, we have demonstrated the effectiveness of different fibres (oligo-fructose, pectin and b-glucan) on promoting satiety, reducing food and energy intake and weight loss.
Fibre intake can also induce a healthier glucose to insulin ratio. Such responses (with pectin) are dose-dependent in rats and it appears evident that effective levels are equivalent to the human Recommended Daily Allowance (RDA).
Increased gut health is a further benefit seen with added fibre as short chain fatty acids produced in fermentation are linked with cancer-protective effects.
In contrast, sustained high levels of protein are thought to be detrimental to both renal and colonic health, but the inclusion of sufficient dietary fibre may counteract some of the adverse effects seen in the gut.
Consequently, this research is seeking to establish the effects increased fibre and protein intake can have on our bodies, both separately and together.
It is important to establish and undertake this research in a suitable animal model, where diets can be precisely controlled and avoid dietary compliance issues that are often seen in human studies in order to obtain clear results.
Soluble fibres from different sources including pectin, oligo-fructose and b-glucan (that have different compositions and structures) were assessed for their effects on satiety and reducing body weight.
Pectin (a galacturonic acid polymer) is present at highest levels in citrus fruit, apples and carrots but is also in other fruit and vegetables, and is sold purified as a health supplement. b-glucan (a branched glucose polymer) is found in bran and cereals.
Oligo-fructose (a fructose polymer) is present in fruits and vegetables, such as bananas, onion, chicory, garlic, asparagus and leeks, and is also sold as an artificial sweetener health product.
We found the decrease in fat levels was greater with increased pectin intake levels in the diet.
Studies on obese rats, fed on a high fat diet, demonstrated that a high fibre (pectin), not a high protein (casein a protein from milk, or a pea protein) diet prevented fat gain over a four week period.
Feelings of fullness are preceded by release of hormones from the gut to inform the brain of sufficient intake. These results are further supported by increased levels of such plasma satiety hormones in animals on the high fibre diet compared to those on a high protein diet.
In addition, glucose metabolism also tended to be improved by a high fibre rather than high protein diet. Fermentation in the large intestine was shown to be affected by added fibre and to some degree by added protein (pea protein more than casein).
The products of fermentation (short chain fatty acids production) are thought to drive satiety hormone signalling, and increased fibre appears to have the biggest effect, although smaller but still significant increases occurred with increased protein (pea protein).
Recent claims have suggested that obesity may be caused by the bacteria in our gut. Our most recent work has indicated that this is unlikely and it is more likely that the changes in bacteria reported in high fat diet studies were due to a different level of fibre intake in the control compared to the high fat diets.
It is known that diet varies with deprivation where the most deprived tend to have the poorest diets containing more sugar and fat and less fruit, vegetables and dietary fibre.
Poor diets contribute not only to being overweight and obesity, but also to related diseases such as heart disease, Type 2 diabetes, hypertension, stroke and some cancers. The cost of obesity to the Scottish society may be as high as £4.5 billion per year.
We have shown that fibres (such as pectin) are effective at enhancing satiety and reducing weight gain as fat in rats. Furthermore, pectin appears more effective than high protein for increasing satiety, decreasing caloric intake and fat storage while on a high fat diet.
This research suggests that sustained increases in fibre intake (such as pectin) even only at human RDA levels may be a better approach than high protein diets for weight loss in obese individuals.
Increased satiety hormone levels may underlie short term post-meal protein-induced fullness, but our results indicate that longer term increases in satiety hormone levels are better sustained by increased dietary fibre intake.
Furthermore, lean mass was better retained on a high fibre (pectin) diet in rats than those fed solely high protein diets; an approach which is more desirable for weight loss strategies.
A high fibre (pectin) diet was also found to have positive effects on glucose-insulin ratios and gut health indicating this strategy could have further health effects against such diseases as diabetes and cancer.
Altogether our data indicates that a high fibre diet may be healthier and more effective than a high protein diet for weight (fat) loss in obesity.
LocationThe Rowett Insitute
- Dr Daniel Drucker, Lunenfeld Tanenbaum Research Institute, Canada.
- Prof Herbert Herzog, Garvan Institute of Medical Research, Australia.
- Effects of Dietary Fibre (Pectin) and/or Increased Protein (Casein or Pea) on Satiety, Body Weight, Adiposity and Caecal Fermentation in High Fat Diet-Induced Obese Rats
- Soluble Fermentable Dietary Fibre (Pectin) Decreases Caloric Intake, Adiposity and Lipidaemia in High-Fat Diet-Induced Obese Rats
- Dose-Dependent Effects of a Soluble Dietary Fibre (Pectin) on Food Intake, Adiposity, Gut Hypertrophy and Gut Satiety Hormone Secretion in Rats.
- Different Types of Soluble Fermentable Dietary Fibre Decrease Food Intake, Body Weight Gain and Adiposity in Young Adult Male Rats
- Dietary Uncoupling of Gut Microbiota and Energy Harvesting from Obesity and Glucose Tolerance in Mice