Sea Buckthorn Decreases and Delays Postprandial Insulin Response in Overweight and Obese Males
Hyperinsulinemia, dyslipidemia, and endothelial dysfunction are caused in part by frequent and repeated postprandial (after meal) hyperglycemia (high blood sugar). These conditions contribute to cardiovascular disease, type 2 diabetes mellitus, and overweight/obesity. Foods with a low glycemic index, such as a variety of berries, may reduce postprandial glycemia, improve acute insulin secretion, and improve appetite control (due to fiber content). The new Nordic Diet (NND), recently developed, emphasizes more calories from plants, fewer calories from meat, and a greater intake of foods from the sea, lakes, and wild countryside. In particular, locally grown or wild berries native to the Nordic countries, especially strawberry (Fragaria × ananassa, Rosaceae) fruit and sea buckthorn (Hippophae rhamnoides, Elaeagnaceae) fruit, are an important flavor constituent of the NND. The energy density of sea buckthorn is approximately twice that of strawberry, primarily due to a high content of unsaturated fatty acids; the amount of fiber in sea buckthorn is 3 times higher than in strawberry. The NND is associated with weight loss and improved insulin sensitivity. Other studies have reported inconclusive results regarding the effect of berries, strawberry, and sea buckthorn on postprandial glycemia and insulin levels. However, according to the authors, Nordic berries have not been evaluated. Hence, the purpose of this randomized, controlled, investigator-blinded, 3-way crossover study was to evaluate the effects of strawberry and sea buckthorn grown in Denmark on postprandial glycemia and insulin levels in otherwise healthy overweight or obese men.
Healthy men (n = 20; mean age, 28.2 ± 7.3 years) with a body mass index (BMI) of 25-35 kg/m2 were recruited via social media in Copenhagen, Denmark. Excluded subjects had “clinical conditions” or obesity surgery, had chronic/frequent medication use, recently (< 3 months) donated blood, participated in other human intervention studies, participated in strenuous physical activity > 10 h/week, habitually consumed > 14 alcoholic drinks/week, acknowledged a history of present or past drug abuse, or were smokers. Subjects received the following 3 treatments: 120 mL of water and (1) 150 g sea buckthorn (picked from wild habitats in Northern Jutland, Denmark) plus 35 g sucrose made into a smoothie, (2) 150 g strawberries (delivered by Rokkedyssegård; Værløse, Denmark) plus 35 g sucrose made into a smoothie, and (3) a non-berry control smoothie containing 35 g sucrose and 8.8 g fructose. The nutritional content was adjusted so that all 3 treatments had similar total energy, protein, and fat.
There was a 2-day washout between each treatment where subjects ate an ad libitum meal of pre-prepared toast with cheese and ham and 300 mL water. For the ad libitum meal, subjects were instructed to eat until they were pleasantly satiated and to ingest all the water; the ad libitum meal was prepared exactly the same each time, and the food was weighed before and after consumption to assess energy intake. At baseline, 30, 45, 60, 90, and 120 min after consuming the test meal, blood was drawn for glucose and insulin analysis; a visual analogue scale (VAS) questionnaire also was administered at each of these time points to measure subjective appetite. A VAS questionnaire was also given 140 min after the ad libitum meal. A VAS questionnaire concerning meal perception (i.e., taste, appearance, etc.) was given after all meals. Subjects were instructed to avoid berries throughout the study period and to avoid alcohol, coffee (Coffea spp., Rubiaceae), medications, and strenuous physical activity 2 days prior to the test days.
Two subjects dropped out of the study citing lack of time. Overall, the subjects had a BMI of 25.7 to 34.4 kg/m2 (mean, 29.3 ± 2.3 kg/m2) and healthy blood pressure (mean systolic, 124.1 ± 5.9 mmHg; mean diastolic, 75.7 ± 5.5 mmHg). Fasting glucose, insulin, and body weight did not differ between visits. The glycemic profile (GP) (time in minutes where blood glucose concentration is > baseline concentration divided by the incremental peak value of blood glucose) was significantly different among treatments (P = 0.016). Sea buckthorn significantly improved GP compared with control (P = 0.0094). In contrast, GP was not significantly different between strawberry and control (P = 0.82). Sea buckthorn significantly lowered plasma insulin concentration by 39.6% at 30 min (P < 0.01) and by 16.5% at 45 min (P < 0.05), compared with control. In contrast, insulin concentration was not significantly different between strawberry and control (P > 0.05). The maximum increase in plasma insulin was significantly different among treatments (P = 0.002). The maximum increase in plasma insulin was significantly 23.6% lower for sea buckthorn compared to control (P < 0.01). In contrast, strawberry did not significantly affect the maximum increase in plasma insulin compared to control (P > 0.05).
Meal sequence had no effect on any of the results. There were no significant differences among groups in the appetite parameters, except sea buckthorn increased the desire for something sweet (possibly because it was tart). Subjects preferred strawberry significantly more than the other treatments (P < 0.001), and sea buckthorn was preferred significantly more than the control treatment (P = 0.001 for scent and P < 0.05 for appearance). However, meal perception had no effect on subjective appetite.
The authors conclude that sea buckthorn decreased and delayed the insulin response; however, the mechanism of action is unknown. Also, there was no effect of strawberry or sea buckthorn on postprandial plasma glucose concentrations in this population. The authors hypothesize that the results of this study may differ from other studies due to the preparation of the berries. In this study, the berries were frozen, defrosted, and pureed. Other studies used dried berries and crushed berries, which may have higher levels of secondary metabolites released from the seeds. Overall, the authors conclude that sea buckthorn may be useful for lowering meal insulin response. However, this was an acute study, so chronic effects must be evaluated to verify this effect. A limitation of the study is that there was no standardized meal the evening before each test, which could have affected glucose and insulin responses, as well as the appetite responses. Other limitations include the small sample size, lack of double-blinding, and that only men were included. The authors report no conflict of interest. The study was supported by the Nordea Foundation; Copenhagen, Denmark.
Mortensen MW, Spagner C, Cuparencu C, Astrup A, Raben A, Dragsted LO. Sea buckthorn decreases and delays insulin response and improves glycaemic profile following a sucrose-containing berry meal: a randomised, controlled, crossover study of Danish sea buckthorn and strawberries in overweight and obese male subjects. Eur J Nutr. October 11, 2017; [Epub ahead of print]. doi: 10.1007/s00394-017-1550-8.