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Green gold: bioactive plant foods

Nowadays, everything must be good for something, must have a direct noticeable or tangible effect. The ever topical issue of nutrition is no exception. All this makes functional food a promising and inexhaustible market. Teams of scientists around the world are focussing on how unhealthy food can be made healthy. Bioactive plant foods are expected to close a gap that should not have existed in the first place.

Prof. Dr. Daniel König © private

The human being is generally considered to be a creature of habit; people and their intestinal tracts prefer to consume food they know and have eaten for decades since childhood. However, foods that are available on the market are not always good for us, and can lead to obesity, disease and accelerated ageing of the body. Diet-related lifestyle diseases such as diabetes and metabolic syndrome are becoming more common and a growing number of people suffer from food intolerance and allergies. Bioactive foods are therefore experiencing a huge boom and the expectations placed on them are relatively high. They are expected to taste good and also contribute to preventing and even treating certain diseases.

“Plants have a very valuable function for humans. This is due to their natural ingredients,” said Professor Dr. Daniel König, internist and nutrition expert at Freiburg University. “They are good for us and enable us to lead a healthy life.” This is why plants are bred, broken down into their component parts and analysed; compounds with a positive effect on human health are extracted, pressed into pills or added to other foodstuffs. Moreover, personalised nutritional advice based on genetic data has the potential to help prevent certain diseases in particular risk groups.

Plant compounds as therapeutics

Ethyl 2-methylbutyrate is a polyphenol found in apple. © Stephanie Heyl

It has been known for some time now that secondary plant compounds (carotenoids, polyphenols) have an antioxidative and anti-inflammatory effect. Epidemiological studies have shown that the risk of contracting colon cancer is associated with lifestyle factors such as the lack of physical activity and a low-fibre diet. The market is reacting to such findings by increasingly offering probiotic yogurts with bifidobacteria, which normally live in the intestines, to restore “good bacteria” or improve our intestinal bacterial flora in general. Prebiotics (dietary fibres) like inulin are added to sausages or muesli with the aim of specifically stimulating bifidobacteria to reproduce and be active in the colon. According to Prof. König, omega-3 fatty acids have many health benefits; research shows that they improve the flow characteristics of blood, have a vasodilatory effect and lower the blood triglyceride level, all of which contributes to cardiovascular health. Vitamin C and E are strong antioxidants and have been shown to protect against cell damage and cancer.1 Salt no longer contains only sodium chloride, but also iodine for the thyroid gland and folic acid for the production of healthy blood cells and against neural tube defects of unborn babies. You can also buy flour with added proteins, enzymes, vitamins, minerals and fibres. It is interesting to find out whether all these food additives actually have a higher value for our health, beauty and fitness than normal foodstuffs. This said, the terms “health food, “beauty food” and “brain food” have already existed for a long time.

Can public health be improved with bioactive plant products?

In animal studies, researchers have demonstrated that cruciferous vegetables such as broccoli, which contain high amounts of mustard oil glycosides, decrease the metastatic potential of pancreatic, prostate and breast cancer (see link on right-hand side: “Bioactive plant foods: plant substances against cancer stem cells”). Curcumin, which is responsible for the yellow colour of the popular Indian spice turmeric, has been shown to lower the blood cholesterol level and slow down age-related brain alterations (see link on right-hand side: “Curcumin for the treatment of Alzheimer’s disease and cancer: healthy plant substances and their transport into the body”). It is therefore one of several compounds with the potential of reducing the risk of developing Alzheimer’s. Other researchers have been able to provide evidence for the ability of cloudy apple juice to prevent the development of colon cancer, at least in thin laboratory animals. The preventive effect comes from the suspended particles and the polyphenols (antioxidants) in cloudy apple juice. Resveratrol, a secondary plant compound found in grapes and red wine, is currently being widely talked about due to the fact that researchers have been able to provide evidence for its antioxidative and anti-inflammatory effect. How reliable are these findings and how high an expectation should we place on them with regard to our health?

“We know that antioxidants are good as radical scavengers,” said Daniel König, going on to add “but there are very many factors that need to be taken into account, to the extent that it has not yet been possible to determine the optimal quantity of dietary fibres, vitamins and secondary plant compounds we should eat in order to stay healthy.” He believes that little is yet known about whether individual food ingredients are able to prevent the development of certain diseases. “I do not believe that certain effects can be attributed to a single compound,” said König referring to the positive effects of cloudy apple juice in contrast to clear apple juice. Quite the contrary is in fact the case. Although the researchers found clear differences in the effect of cloudy and clear apple juice, they were nevertheless unable to ascribe the effects to individual apple juice components. The molecular mechanisms are poorly understood, and substantiation of the highly praised protective effects of certain products therefore remains elusive. However, sufficient evidence is available for the fact that people who eat a lot of apples are less prone to developing chronic diseases and colon cancer. König is certain that a fruit’s environment, by which he means natural environment, the soil in which it grows and direct natural sunlight (also known as ‘terroir’), make fruit and vegetables what they are. König is certain that the efficiency and health promoting effect comes from the synergistic effect of the individual compounds. “Although some studies have provided positive results in terms of the health promoting effects of some compounds, we are far from being able to take these findings as evidence-based medicine and use them to provide recommendations to our patients,” said the scientist, expressing his doubts. He has a somewhat critical view of the functionality of foods to which other compounds have been added to enable them to be sold under a ‘health’ label.

“Healthy” hamburgers with inulin

Will hamburgers with added inulin soon be sold? © Stephanie Heyl

Prof. König also highlights the importance of dietary fibre for our intestinal flora and hence general health. In combination with probiotics, inulin, which is a well-known dietary fibre, leads to a lower incidence of inflammatory bowel diseases. People with acute problems such as ulcerative colitis and Crohn’s disease who eat inulin experience measurable positive effects, especially because inulin also strengthens the intestinal immune system. Would it therefore be a good idea to add five grammes of inulin to all foods? There is no evidence that this would help, König says. 

However, bioactive products have been a promising market for quite some time, especially as a growing number of diseases are found to be related to incorrect nutrition. Metabolic syndrome (a combination of medical conditions, including central obesity, high blood pressure, abnormal blood lipid levels, high blood glucose levels, diabetes mellitus) has been shown to be associated with incorrect nutrition, calorie-, fat- and sugar-rich food and lack of physical activity.2 Many consumers have added functional foods to their shopping list, even though such products cost more. Daniel König believes that things are developing in the wrong direction, at least partially. “Food to which vitamin C has been added, to name but one example, gives the consumer the impression that it is healthy, when in fact it is not,” said the nutrition expert who also deals with age-related diabetes. “The other compounds of this particular food item are often incompatible with a healthy lifestyle.”Consumer organisations and associations such as EFSA (European Food Safety Association) and DGE (German Nutrition Society) are very critical of functional food. The DGE says that poor nutrition cannot be counteracted by the consumption of functional products. It also says that it is misleading to sell unhealthy foods with limited nutrient quantities as healthy ones, just because vitamins and fibres have been added. 

“If people ate according to the DGE’s 10 dietary guidelines, then we would not have the problems we are experiencing today,” says König. He is also certain that even sixty-year-old diabetic patients benefit from a fibre-rich diet. He explains why: “Our goal must not be to make unhealthy foods healthy by adding healthy compounds, but to come up with recommendations on which foods to eat, food that is healthy per se and contains health-promoting factors.” Hamburgers with added inulin are certainly not among the recommended products.

1https://www.thieme.de/viamedici/medizin/wissenschaft/radikale.html
2PDF "Wohlstandskrankheit Metabolisches Syndrom" https://www.gesundheitsindustrie-bw.dewww.med.uni-goettingen.de/de/content/service/3473.html

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