SNFS Dialogue

SNFS Dialogue is a series of symposia addressing current topics of interest in the nutrition and food sciences. 

SNFS Dialogue:

Where myths and facts are far apart: sugar, sugar alcohols and sweeteners

On February 6, 2020, SNFS, together with recognized experts, shed light on many questions around the sweet taste of foods and its impact on human health.  

Prof. Dr. Jan Frank, president of SNFS and Professor of Food Biofunctionality at the University of Hohenheim, welcomed the experts Prof. em. Dr. Hannelore Daniel (Professor emeritus of Nutrition Physiology,  TU Munich), PD Dr. Anne Christin Meyer-Gerspach (St. Claraspital/St. Clara Forschung AG, Basel), Univ. Lektor Dipl. Ing. Alfred Mar (Lecturer at BOKU and President of ICC Austria), and the audience to Berlin.

Left to right: Alfred Mar, Hannelore Daniel, Anne Christin Meyer-Gerspach, Jan Frank

Glucose and fructose metabolism: the dose makes the poison!

Prof. Daniel presented the current knowledge about the absorption, metabolism, and (patho-) physiological effects  of saccharose, glucose and fructose. 

In the media, sugars have been presented as ‚toxic', ‚dangerous', pictured as addictive ‚drugs', and been blamed for the ‚obesity epidemic' and many chronic disorders. „Given the bad press“, says Prof. Daniel, „it is not surprising that sugar has such a bad reputation.“ But even after studying in depths and comprehensively the scientific literature, she was puzzled why all media messages are so one-dimensional as they are. 

The disaccharide sucrose (or saccharose) is cleaved during digestion into its two components, the monosaccharides   glucose and fructose, that are then taken up by different mechanisms into intestinal cells. But even though their concentrations in the intestine are similar, fasting blood fructose concentrations in humans are only ca. 30 µmol/L, while blood glucose concentrations are around 5000 µmol/L and thus ca. 166-times higher.  A single dose of 50 g glucose increases blood glucose from 5000 to 8000 µmol/L in 30 minutes, the same amount of fructose raises blood fructose from 30 to only 500 µmol/L, which is equivalent to only about half a gram of the 50 g consumed. This rather small increase in peripheral blood fructose concentrations is as transient as that of glucose and returns to baseline within 1.5 hours. Can this small increase in fructose concentrations be responsible for high blood lipids and even cause fatty liver?

Reviewing the literature on numerous animal studies and human trials, Prof. Daniel observed that the seemingly ‚known' blood lipid increasing effect of fructose is only relevant when fructose is part of a hypercaloric diet, but does not occur when energy intake is adequate. Furthermore, in mice, a more than 30-fold variation in the blood lipid-response of different strains to high-fat/high-sucrose diets can be observed. Of note, mouse models used in experiments measuring blood and hepatic lipids in response to sugar intake, such as C57BL/6, are among those reacting most sensitive with increased blood lipids.

This raises the question if mice are an aequate model for humans in studying the effects of sugars on lipid metabolism. The hepatic expression of fatty acid synthase, the enzyme responsible for converting sugars to fatty acids, is low in humans and 30-fold higher in C57BL/6 mice and mouse trials therefore likely overestimate the effects in humans. This is in agreement with the results from a meta-analysis comparing the impact of fructose consumption on body weight, fasting and postprandial blood lipids, glycemic control, insulin sensitivity, blood pressure and more. In this analysis, fructose did only impact these parameters as part of a hypercaloric diet, but not when energy intake was adequate. 

Prof. Daniel concluded that sugar has become a symbol for negative health effects like no other food ingredient and that this, at least in part, is owed to the negative representation of sugar - in text and images - in the media. Nearly all scientific studies identified the energy provided by sugars, not the sugars themselves, as the key problem. Therefore, reducing sugar intake will only have a positive health impact if energy intake is reduced at the same time, but not when energy from sugar is replaced with energy from other nutrients.  

The latest in sugar research: sucrose and its potential replacements

PD Dr. phil. II Meyer-Gerspach reviewed the role of sugars and sweeteners on appetite regulation and metabolic effects. 

Appetite regulation is a complex process involving many organs and signalling pathways, in which the enteroendocrine cells in the intestine play an important role. These cells express receptors, similar to the taste receptors on our tongues, and can sense sweet compounds and trigger the secretion of satiety hormones. Also the microbiota, the community of microorganisms living in our intestine, metabolizes sugars, sugar alcohols, and non-caloric sweeteners and produces metabolites that can impact appetite regulation. 

While sugars (sucrose, glucose, fructose) provide energy (4 kcal/g), sugar alcohols and non-caloric sweeteners provide less or no energy and may thus appear to be an excellent alternative to reduce the energy intake from sugars. "But there are still plenty of open questions concerning the impact of sugar substitutes on satiety, satiety hormones, blood glucose and insulin, reward centers in the brain, and gut microbiota“, says PD Dr. Meyer-Gerspach.

The differences between sucrose, glucose and fructose in blood glucose and insulin responses are well known. While sucrose and glucose (single dose of 50 g) acutely increase blood glucose and insulin, the same amount of fructose has a much lower effect. The opposite is true for the inflammatory marker C-reactive protein and blood lipids, which acutely increase upon fructose, but not sucrose or glucose intake. While glucose can be used by all human cells, fructose is almost entirely metabolized in the liver, and therefore exhibits different biological effects.

PD Dr. Meyer-Gerspach investigated the satiety hormones GLP-1 and GIP in a human trial and observed that fructose, opposed to glucose, did not trigger their release. Fructose furthermore did not activate reward centers in the brain and even worse: seems to stimulate regions that are rather associated with appetite, which is in line with other recent publications in this field. Similar effects can be found in the literature for non-caloric artificial sweeteners, which do not trigger satiety hormone secretion and do not activate reward centers in the brain. 

The sugar alcohols xylitol (2.4 kcal/g) and erythritol (0 kcal/g), on the other hand, provide less or no energy. In a study with ten lean and ten obese subjects, PD Dr. Meyer-Gerspach observed that xylitol ingestion leads to a mild and erythritol to no increase in blood glucose and insulin at all, while both sugar alcohols triggered the secretion of satiety hormones and slowed gastric emptying similar to glucose. In a follow-up study, she also saw that both sweeteners activated areas in the brain that are involved in motivation and reward processing. 

PD Dr. Meyer-Gerspach concluded that sugar, when consumed in high amounts and as part of a hypercaloric diet, may negatively affect health and contribute to obesity and disturbances in blood lipids, vascular function, and glucose metabolism. She recommends a reduction in sugar intake, which can be achieved, in part, by replacing it with sugar alcohols or non-caloric sweeteners. However, the goal should not be a 1:1 replacement, but rather a general reduction in the intake of sweetened food. 

She also points out that each sweet tasting agent – whether it is a sugar or a sugar substitute – has its own characteristic metabolic profile. Hence, the effects of their acute and chronic intake need to be studied in detail for each single substance.

Technology of sugars, sugar alcohols, and non-caloric sweeteners in pastry 

University lecturer and ICC Austria president Alfred Mar explained why replacing sugars in foods, in particular baked goods, is not an easy task. 

In light of the increasing awareness in the general public that energy-dense diets may lead to overweight and obesity and that sugar in foods is a significant source of energy, there is a general wish to reduce the energy and sugar contents of foods without changing their sweetness. Sugar alcohols have a similar sweet taste and can thus easily replace  sucrose, but may have laxative effects when frequently consumed. Non-caloric sweeteners, on the other hand, are often much sweeter and are thus used in much smaller quantities. The difference in mass needs to be replaced with other ingredients. In beverages, this can easily be achieved with water. In pastries, however, the missing volume would have to be substituted by either increasing the content of the other energy-pr ingredients (butter, flour, eggs etc.) or by adding bulking agents, such as cellulose and other dietary fiber.

Alfred Mar showed recipes for reformulated pastries in which the sugar was replaced by either sugar alcohols or non-caloric sweeteners and the mass was replaced by either flour and water or flour and egg. In both cases, the reduction in energy was moderate, ca. 5 % and ca. 10 %, respectively. In case of the sugar alcohols, which would make up ca. 30 % of the final product, the warning „excess consumption may have a laxative effect" would need to be added.

Sugars in pastry have a number of technological functions. In addition to their primary role as a sweet flavour, they are a source of fermentable energy for yeast, contribute to browning and crust formation, stabilize foams (e.g. in meringue), and bind water and thus reduce microbial growth and increase shelf life. Sugar alcohols and non-caloric sweeteners can easily substitute the sweet flavour, but do not act as nutrients for yeast, contribute to browning, stabilize foams or increase shelf life. Reformulation aims to reduce the energy content of foods by at least 30 %. In pastries, this is difficult to achieve without significantly impairing the sensory and technological quality of the final product. Alfred Mar therefore concluded his presentation with a very simply recommendation: „Enjoy the original product with sugar and simply eat a somewhat smaller portion. A 30 % reduction in energy is thus easily achieved, while the pastry still gives 100 % of the pleasure.“

Concluding remarks

In the SALUX project, Prof. Frank reported, volunteers complained that yoghurts are generally too sweet. When given yoghurts with increasing amounts of sugar, however, the volunteers picked the one with the highest sugar content as the tastiest. 

Apparently, the consumer demands sweet products and a first step to reduce sugar intake in the general population would require changing sweet perception. As a member of the audience suggested, two weeks of fasting will reset the sweet (and salty) taste, as people often report that foods are too sweet and salty after fasting for a longer period. This, although desirable, will be almost impossible to achieve in the general population. Slowly reducing the sweetness of foods would perhaps be another option, but would require a concerted effort of all food producers and result in the constant need for new recipes, which is unrealistic. 

Prof. Frank closed this very informative SNFS Dialogue and thanked the experts for the interesting presentations and the audience for the many insightful questions and comments. 

He summarized the afternoon as follows:

  1. Sugar (sucrose, glucose and fructose) is viewed as the cause of numerous health problems by many and this is frequently mirrored in the media. 
  2. The negative health effects of sugars, however, are a consequence of an excessive intake of energy and the resulting dysregulation of physiological pathways.
  3. Sugar, when eaten as part of a balanced and energy-adequate diet, is not unhealthy. 
  4. Sugar alcohols and non-caloric sweeteners may be interesting alternatives, but their impact on satiety and physiological processes are in some cases promising, but largely unknown and much more research is required. 
  5. Replacing sugars is not an easy task, as sugar serves technological functions that cannot easily be taken over by sugar alcohols and non-caloric sweeteners.
  6. The consumer currently demands sweet foods and reducing the threshold for sweet perception may be a good strategy for individuals who wish to reduce their sugar intake. 

Past SNFS Dialogue:

Food intolerances and allergies - Lifestyle diseases or metabolic disorders of increasing importance?

On October 21, 2019, SNFS, together with recognized experts, reviewed "food intolerances and allergies" and examined the diverse adverse reactions to foods, their pathophysiological basics, frequencies in the population, and agreed on recommendations for actions. 

Fructose intolerance, lactose intolerance, celiac disease, non-celiac gluten sensitivity, allergies to milk protein, fish, nuts and so on... More and more people, or so it seems, report that they do not tolerate one or more food items in their diets. This is mirrored by a growing number of "Free of"-foods offered in supermarkets.

The causes of these food intolerances are manifold, as are their symptoms. The constant presence of nutrition topics and cooking shows in the media and the resulting growing awareness of consumers for health and nutrition topics may contribute to a heightened sensitivity of the population and increasing numbers of self-diagnosed intolerances and allergies. 

Prof. Dr. Jan Frank, President of SNFS and Professor of Food Biofunctionality at the University of Hohenheim, chaired the event and the lively discussion around the topic among journalists, nutrition experts and the general public. 

Dr. Claudia Laupert-Deick, Head of the Practice for Nutrition Therapy and Coaching in Bonn, talked about the current trends towards food intolerances and explained for whom it really makes sense to omit foods. "More and more people believe that they can no longer tolerate certain foods. But this assumption cannot be confirmed scientifically“, she affirmed. But for humans without a diagnosed allergy or intolerance “Free of “-products do not necessarily provide a health benefit; on the contrary. If, for example, gluten (from wheat) is eliminated from the diet, the consumption of whole grain products and simultaneously of dietary fibre may be reduced. Only a small percentage of the German population has a food allergy. Dr. Laupert-Deick stressed: "It requires a differentiated procedure to diagnose food intolerances and to treat them properly and in a health-promoting way".

Prof. Dr. Jörg Kleine-Tebbe from the Allergy and Asthma Center Westend in Berlin spoke about food allergies and intolerances and highlighted the boundary between fashionable indisposition and life-threatening disease. "Food allergies are immunological reactions against food constituents," he explained. One differentiates between primary and secondary food allergies. "Primary food allergies manifest early in life, in infants and young children, and are immunological reactions to proteins from e. g. cow milk, chicken eggs, wheat, peanuts, tree nuts and fish", the expert said. Secondary food allergies are different, Prof. Dr. Kleine-Tebbe explained: "They manifest later in life and typically in persons who are allergic to airborne allergens, such as pollen. The presence of structurally related allergens in foods then causes the cross-reactivity also referred to as secondary food allergies." Even though 14% of the European population have a self-reported food allergy, only 1% of the population has this confirmed by a physician through the presence of antibodies in the blood. However, only 0.2% of Europeans show allergic reactions when ingesting the respective allergen. Prof. Kleine-Tebbe concluded: “The presence of antibodies alone does not make an allergy. Only in combination with allergic reactions to the food in question, can a food allergy be confirmed.” Avoiding certain foods is only necessary for persons with a confirmed allergy and not recommended for the general public.

Prof. Dr. Nanette Ströbele-Benschop from the Institute of Nutritional Medicine at the University of Hohenheim talked about the psychological and social aspects of food intolerances and allergies. People suffering from these disorders find themselves in a difficult situation: "Depending on the severity of the food allergy, the emotional and social burden can be very high, in particular for sick children and their relatives - especially the mother", she stressed. Children may be singled out at social events as the “odd ones who need a special diet” and parents may experience the need to explain the dietary restrictions of their children to strangers and caterers as stressfull. Or they may suffer from anxiety when being forced to leave the welfare of their children, who may suffer life-threatening consequences upon exposure to, for example, peanuts, in the hands of others. The quality of life of allergy patients and their close relatives may be severely reduced, studies find. But the extent of the psychological burden is rarely recognised or properly addressed by physicians, who focus on treating the allergic reactions. “Tending to the psychological component in order to reduce the emotional burden, may be just as important for ensuring the wellbeing and health of patients in the long run”, concluded the expert.

Overview speakers and presentation titles: 

Dr. Claudia Laupert-Deick (Practice for Nutrition Therapy and Coaching, Bonn): 
Nutrition trend Food intolerances - For whom does it really make sense to omit food?

Prof. Dr. Jörg Kleine-Tebbe (Allergy and Asthma Center Westend, Medical Practice Hanf, Ackermann & Kleine-Tebbe, Berlin): Allergies and food intolerances: between lifestyle diseases and death risk

Prof. Dr. Nanette Ströbele-Benschop (University of Hohenheim, Institute of Nutritional Medicine, Stuttgart): Psychological and social aspects of food intolerances and allergies

Publications cited by the speakers:

Prof. Dr. Kleine-Tebbe:

Prof. Dr. Ströbele-Benschop:

Further information can be found here:

  • German Society for Allergology and Clinical Immunology (Deutsche Gesellschaft für Allergologie und klinische Immunologie):
  • Deutscher Allergie- und Asthmabund (German Allergy and Asthma Association):

Press release:

Please read the joint press release of SNFS and the University of Hohenheim for further details.

Past SNFS Dialogue: 

Fats and oils in foods - from food technology to nutritional physiology


On February 20, 2018, SNFS, together with dedicated experts,  shed some light on the importance and role of fat in the diet and foods. Why do we need fats in our diet? What is their role in health and disease? Do we eat too much or the wrong kinds of fats? Why are certain fats frequently used by the food industry? These questions and more were addressed by our experts Dr. Sarah Egert, Professor Stefan Lorkowski and Professor Eckhard Flöter and intensively discussed with the audience. 

Prof. Dr. Jan Frank, President of SNFS and Professor of Food Biofunctionality at the University of Hohenheim, moderated an intensive discussion on the topic of fats with many nutrition and food scientists, journalists and representatives of professional societies and associations. 

"It is not the quantity but the quality of the dietary fats that is decisive for human health," concluded the nutrition and food experts at the end of the event. And palm fat also fulfils important technological functions in many foods and therefore cannot be easily replaced. 

Speakers and presentations:

PD Dr. Sarah Egert (German Nutrition Society & University of Bonn): 
The role of fats in nutrition

Prof. Dr. Stefan Lorkowski (University of Jena): 
Fats: What do nutrition societies currently recommend and do we need to reformulate recommendations based on findings from recent studies?

Prof. Dr. Eckhardt Flöter (Technische Universität Berlin):
The food technology of fats

Please read the joint press release (in German) of SNFS and the University of Hohenheim for further details.

Past SNFS Dialogue: 

Communication between scientists and (science) journalists - Pitfalls and solutions

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Simplifying scientific data and  and communicating them through media to the general audience without distorting the findings can be a challenge for both scientists and journalists. This symposium was held September 22, 2016, in Berlin and brought together researchers and (science) journalists, highlighted pitfalls and present some solutions for improved communication between them to ensure accurate presentation of research and scientific findings in the media.

Speakers and presentations:

Prof. Dr. med. Jörg Hasford (Ludwig-Maximilians-University of Munich)

presented common types of human studies, explained basic principles and methodology and gave an overview of their significance and permissible and impermissible conclusions.

Kathrin Zinkant (Editor in the Knowledge Department of the Süddeutsche Zeitung):

talked about her work as a science journalist and explained how she selects scientific topics for the media, reviews study results and conclusions and prepares them for the reader.

Prof. Dr. Peter Stehle (Institut für Ernährungs- und Lebensmittelwissenschaften, Rheinische Friedrich-Wilhelms-Universität Bonn

talked about his personal experiences as a scientist in his communication with journalists and how he prepares and presents his research data for journalists.

Click here to read a brief report (in german) on this SNFS Dialogue.