Abstract
Purpose: Flaxseed can be effective at lowering and stabilising blood glucose responses. The aim of this study was to determine whether flaxseed could lower blood glucose response more effectively when consumed as a single portion of 30 g, or a split portion consumed three times per day (10 g flaxseed per portion). Methods: The study was a randomised, repeated measures, cross-over design. Fifteen healthy participants consumed either (1) three flaxseed muffins containing a total of 30 g of flaxseed once in the morning, (2) three flaxseed muffins consumed at three different timepoints across the day (10 g flaxseed per muffin) or (3) three control muffins consumed at three different timepoints across the day (0 g flaxseed). The 24-h blood glucose response was measured using a continuous glucose monitor. Results: The results of this study demonstrated that flaxseed muffins given three times a day were effective at lowering and maintaining blood glucose levels over 24 h, compared to the control muffins and that both flaxseed treatments resulting in a lower blood glucose iAUC during the night. Conclusion: The results of this study indicated that adding flaxseed to a daily diet produced a lower glucose profile over 24 h in a free-living context compared to the control muffins.
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Key Points
There is a considerable body of evidence indicating that the consumption of low glycemic index (GI) foods reduce blood glucose fluctuations, and benefits the management and prevention of diabetes and prediabetes. Low GI foods help to stabilise blood responses at a normal level for longer period of time minimising potentially large fluctuations in blood glucose levels.
Flaxseed is considered to be one of the key plant sources of dietary fibre, as it contains both soluble and insoluble fibre with a ratio of soluble to insoluble varying between 20:80 and 40:60. The soluble fibre in flaxseed is mucilage gum and insoluble fibre is cellulose, hemicellulose and lignin. The question remains as to whether flaxseed is more effective at maintaining blood glucose at the normal level over 24 h when the portion is given once or spread out throughout the day. The majority of studies on flaxseed and glycaemic response gathered the data in a laboratory setting the morning after an overnight fast, which does not represent the physiological responses across a full day.
Continuous glucose monitoring systems (CGMS) provide a method of evaluating subcutaneous interstitial fluid glucose over a number of days, by applying an electrochemical detector under free-living conditions. CGMS evaluates interstitial glucose concentrations every 5 min and are minimally invasive, which gives an opportunity to evaluate the direction, magnitude, duration, frequency and causes of fluctuations in blood glucose levels.
In the current study, the flaxseed portion was split over the three meals, which may cause a lower blood glucose post each of the three meals. The aim of this study, therefore, was to determine the most effective timing of flaxseed consumption to lower blood glucose response in healthy participants. This study used a single and a split portion regimen and investigated the blood glucose response over a 24-h period using a CGMS to determine whether flaxseed was more effective when consumed as a single portion of 30 g or as a split portion consumed three times per day (10 g flaxseed per portion).
The results of this study demonstrated that flaxseed muffins given 3 times a day were effective at lowering and maintaining blood glucose levels over 24 h, compared to the control muffins and that both flaxseed treatments resulting in a lower blood glucose iAUC during the night.
Although the results of the current study did not show differences after each of the individual meals, this effect is applicable to the current study as the results of iAUC over 24 h was significantly lower when flaxseed muffins were consumed once a day, as well as when they were split across the day, compared to the control.
The flaxseed muffins contained 4.9 g/100 g of fibre, which could be one of the main reasons for the changes in blood glucose seen in the current study. Flaxseed contains n-3 fatty acids alpha-linolenic acid has which has previously been shown to have a positive impact upon glycaemic control. It has been shown that flaxseed lignan secoisolariciresinol diglucoside restricts expression of the phosphoenolpyruvate carboxykinase gene, which is considered the main enzyme in glucose synthesis in the liver. The richest source of plant lignans is flaxseed which incorporates approximately 75–800 times more lignans in comparison to cereal grains, legumes, fruits and vegetables.
The current study also investigated gastrointestinal symptoms compared with the control muffins and found that flaxseed muffins of both treatment regimens caused some side effects on the gastrointestinal system. These results suggest flaxseed muffins can cause some gastrointestinal side effects, although they were not severe as the highest mean value was only 1.9 on a scale of 1–10. The results of this study indicated that adding flaxseed to the diet can produce a lower glucose profile over 24 h in a free-living context compared to the control muffins. Furthermore, flaxseeds were effective in improving the blood glucose profile over the 24 h; however, to improve blood glucose both over 24 h and overnight flaxseeds are better consumed in smaller amounts dispersed throughout the day. This study provides important data about adding flaxseed to the diet for healthy individuals, which can improve glycaemic response throughout the day and overnight.