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It's all about the fiber

Doctors newspaper online, 14.01.2019

Mega study

Significantly fewer heart conditions, tumors and diabetes: the more fibers, the longer life – and the whole grain scores against colorectal cancer. That is what the biggest study so far probably says about the subject.

By Thomas Müller


Dried fruit is rich in fiber, as are whole grains and legumes.

© photocrew / stock.adobe.com

The most important in short

ask: How many fibers should adults use every day?

answer: At 25-30 grams per day, the incidence of colorectal cancer, diabetes and cardiovascular disease is 15-30% lower than with a consumption of less than 15 grams.

which means: A high fiber diet can prevent relevant widespread diseases.

constraint: A causal relationship can not be demonstrated, a high-fiber diet is probably associated with a healthier overall lifestyle.

DUNEDIN / NEW ZEALAND. There is of course a simple recipe against most lifestyle diseases: eat more fiber! Anyone who consumes between 25 and 30 grams per day has a significantly reduced risk of cardiovascular disease, bowel tumors and diabetes – and of course lives longer.

Whether fiber is actually responsible for such positive effects, however, the evaluation of all relevant nutritional studies can ultimately not prove – it is likely that other ingredients of a high fiber diet are crucial.

Nutritionist around Dr. However, Andrew Reynolds of the University of Dunedin in New Zealand found clear dose effects in her mega-analysis: the more fiber optic consumers consume, the lower their data point to the risk of major civilization diseases. "This suggests that the association with various non-communicable diseases might be causal," they write in their publication in "Lancet" (doi: 10.1016 / S0140-6736 (18) 31809-9).

Mortality rate reduced by 15%

For the analysis, the researchers evaluated a total of 185 publications on prospective observational studies and results from 58 randomized clinical trials. The observation period of the prospective studies was a total of 135 million person-years, in the clinical studies more than 4600 people participated. The researchers around Reynolds have only thought about studies in which the participants did not have chronic diseases at the beginning.

All observational studies had to provide information on the quantity and quality of the carbohydrates consumed, as well as the mortality rate, the number of cardiovascular events or the incidence of diabetes and tumors. The clinical studies should investigate the effects of carbohydrates consumed on cardiovascular and metabolically relevant factors such as blood pressure, blood sugar and blood lipids.

Risk reduction in numbers

Researchers in observational studies compared subjects with low fiber intake (less than 15 g per day) and people with relatively high consumption (more than 25 g), with a high-fiber diet that has a fairly consistent risk reduction of 15-30% for the main diseases in humans and tumors,

Total mortality by participants with fiber-rich tissue was 15% lower in the course of the studies, the mortality rate by 31% and the CVA mortality rate by 22%. Heart attacks and strokes were 24% and 20% higher in the fiber-rich diet group and 15% less likely to develop type 2 diabetes. Intestinal tumors were 16% less frequently observed and bowel cancer mortality was reduced by 13%.

With the exception of CHD incidence, the effects appear to be slightly more pronounced with fiber levels of more than 30 grams per day. For example, a consumption of more than 40 grams per day is associated with a diabetic rate reduced by about 40%. For the other diseases, however, the event curves decrease considerably with increasing doses, so that consumption of more than 30 grams per day seems to offer little extra benefit.

A similar correlation was found between researchers with regard to whole grains – an important source of fiber. In part, the effects were even more pronounced with high consumption, but above all there was a linear correlation with the colorectal cancer rate: the more whole grains, the less common intestinal cancer.

Glycemic index only makes little sense

In the randomized controlled trials, a high-fiber diet significantly reduced body weight, cholesterol, blood pressure and fasting glucose levels. The same has been observed in a diet with whole grains. In contrast, there was almost no correlation between the diseases studied and the glycemic index and the glycemic burden.

Only the incidence of diabetes and stroke was slightly increased with a high percentage of easily digestible carbohydrates. The researchers around Reynolds conclude that the fiber content says more about the quality of carbohydrates than the glycemic index. According to their data, which should be used as a basis for WHO recommendations, they are of the opinion that fiber consumption between 25 and 30 grams per day is optimal, with higher consumption likely to yield even more benefits.

However, many people already fail at a 25-gram hurdle: in most countries fiber consumption is well below 20 grams per day, with only about 10% taking 30 grams, say the authors of the study.

What should we eat?

In addition to wholemeal products, the pulses are particularly high in fiber, fruit consumed with the skin (apples, pears, plums, apricots) and potatoes cooked with skin.

Dietary fiber increases satiety, improves glucose and insulin metabolism and keeps a beneficial intestinal flora alive. It produces important vitamins, short-chain fatty acids and immunomodulators, which are also involved in the complex communication between the gut and the brain, according to the researchers to consider Reynolds.

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