Health benefits of oat (Avena sativa) bioactives. Acute and second-meal effects of oat polar lipids and beta-glucans.

Popular scientific summary

In recent decades, there has been a significant increase in lifestyle-related diseases, including obesity, type 2 diabetes, and cardiovascular diseases. According to the International Diabetes Federation, there were 536 million individuals diagnosed with diabetes in 2022, and this number is projected to increase to 780 million by 2045. The healthcare systems are under pressure and call for urgent solutions, where prevention, as a sustainable approach, must complement the current paradigm of treatment. Dietary habits are the most important contributing modifiable factors in this context; thus, a healthy diet must be part of successful preventive strategies against cardiometabolic diseases.

Oats (Avena sativa) have been cultivated for thousands of years, but initially it was found as a weed within other cereals such as wheat and barley. Oats are now recognized as a sustainable cereal grain, occupying the sixth position in global grain production rankings. Oats have been grown in Nordic countries since the Middle Ages, and their cultivation substantially increased due to a favourable weather condition for its growth. The gradual unveiling of its nutritional value has resulted in a consistent rise in popularity of oat for human consumption. It contains a treasure of potential health-promoting bioactive compounds, such as polar lipids, soluble dietary fibres like beta-glucans and arabinoxylans, antioxidants i.e. α-tocopherol, and polyphenols such as avenanthramides. Furthermore, oats are an excellent source of high-quality plant-based proteins, vitamins, and minerals. Considering sustainability, global 2030 goals and health aspects, the recent Nordic Nutrition Recommendations 2023 (NNR2023) introduced a new guideline emphasizing consumption of plant-based diets and a reduction of animal-based dietary choices. In this regard, oats are versatile candidates in resolving sustainable dietary choices and can contribute to combat global lifestyle-related diseases.

The current doctoral thesis aimed to explore the health potential of oat-derived bioactive compounds, with a focus on polar lipids and beta-glucans. For this purpose, four intervention studies in healthy participants were conducted. The studies focused on postprandial metabolic effects of formulated test foods enriched with polar lipids or beta-glucans. The test products were consumed at breakfast and cardiometabolic disease-related test markers were measured in blood repeatedly both after the breakfast and after a standardized lunch without the bioactive compounds to investigate so called “second-meal” effects of the bioactives.

The present work demonstrates that intake of oat polar lipids (12 – 15 g) included in a breakfast (liquid or solid meal) has a beneficial impact on blood glucose regulation and circulating triglyceride (TG) concentrations acutely after the breakfast, but also after the standardized lunch meal. Furthermore, oat polar lipids and/or sunflower lecithin have the potential to increase the release of satiety promoting gut hormones such as GLP-1 and PYY, and reduce the release of the hunger-inducing hormone ghrelin. In one of the studies, metabolic effects of oat polar lipids were compared to those of a commercially available plant polar lipid preparation (sunflower lecithin). The results indicated sunflower lecithin exerts similar effects to those of oat polar lipids. Additionally, the results demonstrate that consumption of betaglucans from oats improve postprandial glycaemic responses and subjective appetite sensations acutely after the breakfast and after the subsequent lunch. Another notable observation was that a dose of 2 g of oat beta-glucans might effectively lower the blood glucose peak after a meal, which is appreciably lower than the 4g dosage as stated by the health claim of the European Food Safety Authority (EFSA). This finding may facilitate the development of innovative products for the dietary management of postprandial blood glucose regulation.

This current research thus demonstrates cardiometabolic preventive properties of polar lipids from oats and sunflower, as well as oat beta-glucans, by improving cardiometabolic risk markers both in the postprandial period immediately after consumption and after a subsequent meal lacking the bioactive compounds.

In summary, the thesis shows that the consumption of oat polar lipids included in a meal may enhance the acute and second meal postprandial glucose tolerance, reduce circulating TG, and enhance the secretion of appetite regulating hormones in healthy young adults. Furthermore, it confirms that oat beta-glucans improve the acute glycaemic response, but in addition exert beneficial effects following a second meal. A remarkable observation is that relatively low amounts of oat beta-glucans may reduce blood glucose peaks, in doses below EFSA’s recommended ones. The findings in this doctoral thesis are new knowledge, which can contribute to the development of innovative food products with preventive potential against cardiometabolic diseases.