There is an ongoing scientific debate about the prevention of chronic disease and recognition of the importance of dietary (macro)nutrients. In particular, there is debate
about replacing saturated fats with unsaturated fats or carbohydrates. Excessive consumption of certain carbohydrates can also be a risk factor, and certain carbohydrate-rich foods are also implicated in the rapidly increasing incidence of obesity and type 2 diabetes. This project set out to investigate the " metabolic quality " of carbohydrates, this being how they are used in the body, so that consumption of the most beneficial types can, in future, be encouraged.
Consumption of simple sugars or rapidly digestible starch can lead to a rapid increase in serum glucose levels (high glycemic index foods), an increase in serum insulin levels and increased synthesis of triglycerides. This metabolic response is thought to be detrimental to longer-term optimal health.
One parameter in considering the "metabolic quality" of carbohydrates is the intensity of
the blood glucose response after ingestion or the glycemic index (GI). This is dependent upon a number of physiological processes such as gastric emptying, intestinal transit, glycogen synthesis, glucose production of the liver, stimulation of glucose utilisation and oxidation. These processes need to be monitored and better understood so that the glycemic index of foods and food products can be beneficially modified.
Within the EUROSTARCH project this was achieved by tagging food products and tracking their progress though the digestive tact. This was done through a novel approach using stable isotopes . These isotopes are not harmful for humans and are already naturally present in biological substances. The amount of naturally occurring 13 C in plant materials was increased artificially and by consuming these products, their subsequent digestion and metabolism was traced by measuring the 13 C-glucose in blood, 13 CO 2 in exhaled breath and in 13 C-metabolites that were excreted.
Thus, the aim of EUROSTARCH was to increase the knowledge of various stages in the processes of carbohydrate digestion and fermentation, and to use this knowledge to
further define food products most suitable for the prevention of chronic disease.
2. EUROSTARCH AIMS
The specific aims of this project were:
1 To investigate the metabolic effects of starchy foods related to the rate and extent of digestion of starch.
2 To investigate the biological effects of cognitive function and satiety of starchy foods.
3 To investigate fermentation of resistant starch in the colon.
3. EUROSTARCH INVESTIGATIONS
Detailed scientific investigations were carried out by the EUROSTARCH project teams related to each of the above aims. These included short-term metabolic trials of a low-glycemic (LGI) or high-glycemic index (HGI) breakfast in overweight non-diabetic subjects using different test meals, and the effects of GI and indigestible carbohydrates from the evening meal on glucose tolerance at breakfast.
In addition the effects of a five-week low-glycemic index diet on weight control and cardiovascular risk factors in overweight and otherwise healthy subjects was carried out. After this 5 week nutritional intervention, dietary survey results showed that all subjects in the LGI group reached a low glycemic index. The Low GI diet was associated with:
- a significant weight loss of -1.1 ± 0.3 kg (p= 0.004)
- no changes in fat mass (-0.7 ± 0.6 %, p= 0.15)
- a significant, 10% decrease in total cholesterol (both HDL and LDL), (p<0.001)
- a significant 7% decrease in C peptide (mostly in women) with no change in insulinemia (p<0.05)
The High GI diet was associated with:
- a significant 2.4% decrease in basal glycemia mostly in women (p=0.002)
Full details of all the scientific investigations carried out in EUROSTARCH can be found in the final report of the “Scientific information” page
4. EUROSTARCH RESULTS
Full details of all the published results can be found in the final report of the “Scientific information” page
The main results from the EUROSTARCH project aims include:
Aim 1: Metabolic effects of starchy foods
The production and use of 13 C-enriched substrates , grains and model foods was achieved. Industrial food processing was shown to dramatically modify glucose response. Critical food processing parameters were identified to achieve low gelatinised starch products which resulted in a low glycemic response. With stable isotope techniques more insight was gained about glucose kinetics after the ingestion of starchy foods, and the relationship with hormonal responses. The metabolic response after eating whole-wheat bread is not only determined by the rate of starch digestion, but also by other food factors. Hormone response to rapidly and slowly available carbohydrates is different.
It has also been found that certain low GI-foods which are high in resistant starch and dietary fiber (barley kernels), not only acutely decrease glycemia, but also glycemia after subsequent high GI foods (breakfast to lunch, evening meal to breakfast). These results suggest that events of colonic fermentation of indigestible carbohydrates are involved in modulating glucose tolerance from the evening to breakfast.
Substituting a HGI diet with a LGI diet for 5 weeks has been shown to result in decreased body weight and improved lipid profile in overweight healthy subjects.
Aim 2: Cognitive effects
The cognitive tools developed allowed the detection of differences in cognitive performance, related to the postprandial blood glucose level, and indicated that higher glycaemia in the late postprandial phase resulted in improved cognitive function. The results also indicate that even in healthy elderly subjects, there was a significant
difference in cognitive performance related to the efficiency in blood glucose regulation - subjects with less efficient blood glucose regulation displayed lower scores in the
cognitive tests. Finally, learning ability was enhanced with high blood glucose levels. However, no definitive conclusions could be drawn.
Aim 3: Fermentation in the colon.
Material and tools were developed to study the effect of resistant starch/dietary fiber fermentation on the production of short chain fatty acids, as well as on changes in the microbes in the colon:
13 C-barley with high enrichment makes it possible to trace short-chain fatty acids in plasma and urine.
Analytical methods were developed to measure very low 13 C enrichments in human plasma after ingestion of 13 C -enriched resistant starch.
A non-invasive method using urine samples to measure total acetate production has been successfully applied in the fermentation study.
A non-invasive strategy based on stable isotope technology, focussing on the metabolite ammonia allowed to establish that the ingestion of resistant starch results in a higher
level of removal of ammonia from the colonic lumen.
These techniques now make it possible to study, in detail, the fermentation processes in the colon and relate these to potential health benefits of different diets. Recent studies indicated that the colon plays an important role in modulating whole body energy metabolism. This set of developed techniques can be used for systematically studying complex interactions.
5. IMPLICATION AND APPLICATION OF EUROSTARCH RESULTS
Scientific results will be published in international peer reviewed journals and presented
at international conferences.
In the EUROSTARCH project stable isotope technology was used extensively. This has
led to new function tests (gastric emptying, intestinal transit, colonic function) and analytic procedures which can be broadly applied in future bio-medical practice.
Increased knowledge about digestion and fermentation of starch will be used in dietary advice for healthy people and various patient groups. Increasing consumption of healthy starch products containing slowly digestible starch and fiber might lead to a reduction of chronic diseases like obesity, diabetes mellitus type 2, and cardiovascular diseases.
Consumers will be able to apply this new knowledge and information about healthy starch products to their food choices, which could not only lead to a reduction in the risk of
chronic diseases, but could also lead to an improvement of cognitive functions.
It is known that the efficacy of dietary advice to the healthy population is limited. Therefore,
it is important to explore how the food industry can improve food formulations to make 'healthier' food products, which combined with clear labelling and appropriate marketing could help consumers benefit from this research.
6. OVERALL CONCLUSIONS FROM EUROSTARCH
Results of the EUROSTARCH project confirm that substituting high GI starchy foods with low GI starchy foods has a positive effect on satiety.
Results of the EUROSTARCH project confirm that substituting high GI starchy foods with low GI starchy foods has a positive effect on weight loss.
Results of the EUROSTARCH project confirm that substituting high GI starchy foods with low GI starchy foods has a positive effect on lipid profile, including total cholesterol, LDL cholesterol and LDL/HDL ratio.
There is no conclusive evidence at this stage
Glycemic index (also glycaemic index , GI ) is a ranking system for carbohydrates based
on their immediate effect on blood glucose levels. The glycemic index of a food is defined by the area under the 2 hour blood glucose response curve ( AUC ) following the ingestion of a fixed portion of carbohydrate (usually 50 g). The AUC of the test food is divided by the AUC of the standard (either glucose or white bread) and multiplied by 100.
Low GI: 55 or less
Medium GI: 56 - 69
High GI: 70 or more
Lipid (fat) particles present in blood stream
Isotopes are any of the several different forms of an element each having different atomic mass ( mass number ). Each of the elements that together comprise organic matter (C, H, O, N & S) possess minor stable isotopes that are present at low concentration throughout nature. They are thus naturally present in the body and in the food that we eat. These minor stable isotopes, such as 13 C, are not radioactive and do not present a hazard to the body or in the environment. They have identical biological and chemical properties to their more abundant major isotopes, such as 12 C. We can detect them by nature of their differing mass.
Mental processes such as memory , attention , perception , action , problem solving and mental imagery .
Fermentation in the colon
Fermentation is a process of energy production in a cell in an environment with no oxygen present. Components of the diet that fail to be digested will pass to the large intestine (colon) where they may be fermented by bacteria producing short chain fatty acids, other organic acids such as lactic acid, and gases. Colonic fermentation of resistant starch and other non-digestible carbohydrates produces a number of products that could play important roles in metabolic and physiological processes.
Most of the starch, which is ingested, is digested in the small intestine and absorbed as glucose. However, some starch can escape digestion and arrive in the large intestine where it is usually fermented by colonic bacteria. This fraction of the starch is called “resistant starch”. Indeed it has been defined in 1992 (Asp, 1992) as “the sum of starch and products of starch degradation not absorbed in the small intestine of healthy individuals”. It represents around 2-3% of the total starch of most of the starchy foods, however the fraction of resistant starch may be much higher in some cases.
The ability of various organs (muscle, cells, liver) to remove glucose from the bloodstream.
13 C-enriched substrates
By enriching components of the diet with stable isotope tracers (e.g. 13 C) their nutritional role and metabolic fate can be investigated. In the EUROSTARCH project 13 C-enriched wheat flour was used. This was obtained by cultivating wheat plants for several days in a strictly controlled environment, with the carbon dioxide in the air being replaced by 13 CO 2 . With the same method 13 C-enriched barley was produced.
The process of rendering starches soluble in water by heat is called gelatinization. In this process major structural changes of the starch occur and make the starch more quickly digestible.
Pattern of lipids in the blood. A lipid profile usually includes the total cholesterol, high density lipoprotein (HDL) cholesterol, triglycerides, and the calculated low density lipoprotein (LDL) cholesterol.
Cognitive tools developed were the working-memory and the selective attention test.
This test deals with a memory system that stores and processes information at the same time. The capacity of working memory is limited and in this test the span of the system was determined. The tests were oral and each test comprised of 12 sets of four sentences that could be either correct or incorrect. Immediately after each sentence, orally presented, the subject had to indicate if the sentence was correct or not. After each set of four sentences the subject was told to recall the first word in each sentence. The task was scored for correct recalled words.
Selective attention (SA)
This computerized test consisted of 78 different pictures shown at two second intervals, one by one, on a computer screen. The pictures consisted of a square, divided in four smaller squares. One of the four smaller squares was red and one was green. Each time a new picture emerge on the screen either the green, the red or neither of the coloured squares was in the same position as in the previous picture. The subjects had to mark which of the three alternatives occurred when a new picture emerge. The task was scored for correct responses, and the reaction time.