Oats and blood sugar levels
Oats, also called Avena sativa, were in past and are nowadays one of the most popular cereals for human consumption. The first evidence of oats in the human diet were unearthed by archaeologists in southern Italy and date back approx. 32 000 years ago, well before farming started to develop.1 Since then, oats are widely consumed and used in a variety of food products due to their nutritional value and taste. In some cases this simple cereal acquired a lot of prestige and was much in demand, even becoming a central part of a nation’s cuisine. For example, the Scottish embraced oats as a part of their national dishes and even in the age of fast food the Scots are still very attached to oats in their cuisine. Nowadays oat is frequently consumed as porridge or breakfast cereals, such as muesli or granola. It is also frequently added to yoghurts or desserts or eaten baked, in form of biscuits and breads.2
Whole oat grain contains many nutritionally valuable compounds.3 Oats contain high amounts of vitamins, minerals, unsaturated fatty acids and protein. It is also considered as one of the richest sources of dietary fibre.3 One of the types of fibre present in oats is long-chain molecules called betaglucans. They usually make up 2.5% to 8.3% of the grain mass and this component is known to be responsible for positive health effects attributed to oat consumption.3
The beta-glucans in oats are widely associated with various positive health effects, such as a beneficial impact on blood cholesterol and blood sugar levels.4-6 When added in high enough amounts to a meal containing carbohydrates, beta-glucans lead to the decrease of post-prandial glycaemic responses. In simple terms, it means that when present at doses of at least 4 g in every 30 g of available carbohydrates in a meal, beta-glucans slow down the blood sugar level increase after meal.5 This amount of carbohydrates is present, for example, in a cup of cooked whole-wheat penne pasta, two slices of wheat bread or half a piece of apple pie, while 4 g of beta-glucans is present in 100 g of rolled oats or can be consumed as a food supplement.7, 8 One has to keep in mind that oats are also a source of carbohydrates. Oat bran, which is one of the most nutrient-rich parts of the oat plant in terms of beta-glucans, contains approximately 10 g of beta-glucans per 100 g, but this portion also provides around 67 g of carbohydrates.2, 8 Therefore nutritional supplements could be an easy way to keep a healthy and beneficial balance between beta-glucans and carbohydrates in our daily meals, without increasing consumption of the latter.
A spike in blood sugar levels after a meal is a physiological phenomenon related to the way our body extracts carbohydrates from the food we consume. The intensity of this rise depends mostly on the composition of the food and types of carbohydrates present in it. Usually the more „simple” the carbohydrates are, the more rapid the increase in blood sugar levels is. The blood sugar spike is followed by potent and quick insulin release leading to the sudden drop of blood sugar. On the other hand, the presence of complex carbohydrates is usually related to longer and more sustained blood sugar increase and the corresponding insulin release and following blood sugar decrease. However, there are exceptions to this rule, such as fructose, which has a low glycaemic index despite being a simple carbohydrate or white bread, which contains complex carbohydrates and ranks high on the glycaemic index. The Glycaemic Index, abbreviated also as GI, is a ranking of carbohydrates according to the extent to which they raise blood sugar levels after eating. A high glycaemic index rating means that consumption of a particular food will lead to a rapid blood sugar increase, while consumption of low glycaemic index foods cause more moderate blood sugar increase sustained over a longer period of time. 9 Being aware of the glycaemic index of the food we eat is important for our health. Consumption of foods with high glycaemic index rating is linked to increasing incidence of type 2 diabetes, while a low glycaemic index diet reduces both the glycaemic response and the corresponding insulin release and consequently, may improve insulin sensitivity reducing the risk of the disease.9
But how can beta-glucans, in particular the ones derived from oats, influence blood sugar levels following carbohydrate consumption? One of their most important properties, which is also responsible for health effects related to their consumption, is their viscosity.2 As a result, betaglucans are able to prolong the time it takes for food to be digested in the stomach and then in the intestine, which slows down the absorption rate of sugars and fats.10 That is why blood sugar levels do not increase as rapidly as they would in the absence of beta-glucans. What is also important to note is that this effect is not associated with disproportionately increasing insulin production and it makes consumption of beta-glucans beneficial. 5
- Mariotti Lippi M, Foggi B, Aranguren B, et al. Multistep food plant processing at Grotta Paglicci (Southern Italy) around 32,600 cal B.P. Proceedings of the National Academy of Sciences. 2015;112(39):12075-12080.
- Sadiq Butt M, Tahir-Nadeem M, Khan MK, et al. Oat: unique among the cereals. European journal of nutrition. 2008;47(2):68-79.
- Ben Halima N, Ben Saad R, Khemakhem B, et al. Oat (Avena sativa L.): Oil and Nutriment Compounds Valorization for Potential Use in Industrial Applications. Journal of oleo science. 2015;64(9):915-932.
- Scientific Opinion on the substantiation of health claims related to beta glucans and maintenance of normal blood cholesterol concentrations (ID 754, 755, 757, 801, 1465, 2934) and maintenance or achievement of a normal body weight (ID 820, 823) pursuant to Article 13(1) of Regulation (EC) No 1924/2006. EFSA Journal. 2009;7(10):1254-n/a.
- Scientific Opinion on the substantiation of health claims related to beta-glucans from oats and barley and maintenance of normal blood LDL-cholesterol concentrations (ID 1236, 1299), increase in satiety leading to a reduction in energy intake (ID 851, 852), reduction of post-prandial glycaemic responses (ID 821, 824), and “digestive function” (ID 850) pursuant to Article 13(1) of Regulation (EC) No 1924/2006. EFSA Journal. 2011;9(6):2207-n/a.
- Scientific Opinion on the substantiation of a health claim related to oat beta glucan and lowering blood cholesterol and reduced risk of (coronary) heart disease pursuant to Article 14 of Regulation (EC) No 1924/2006. EFSA Journal. 2010;8(12):1885-n/a.
- Wang Q, Ellis PR. Oat beta-glucan: physico-chemical characteristics in relation to its bloodglucose and cholesterol-lowering properties. The British journal of nutrition. 2014;112 Suppl 2:S4- s13. 8. USDA. USDA National Nutrient Database for Standard Reference, Release 2
- US Department of Agriculture, Agricultural Research Service, Nutrient Data Laboratory 2015.
- Kirpitch AR, Maryniuk MD. The 3 R’s of Glycemic Index: Recommendations, Research, and the Real World. Clinical Diabetes. 2011;29(4):155-159.
- Shen XL, Zhao T, Zhou Y, et al. Effect of Oat beta-Glucan Intake on Glycaemic Control and Insulin Sensitivity of Diabetic Patients: A Meta-Analysis of Randomized Controlled Trials. Nutrients. 2016;8(1).