Research Extracts: Blueberries and Diabetes, Almonds and Your Heart, Sweet Drinks and Cravings
Welcome to the June 2020 edition of Research Extracts. “The Extracts” is designed to keep busy practitioners and savvy consumers up-to-date on the latest research on diet, nutrients, botanicals, the microbiome, the environment, and lifestyle approaches to good health. Our medical team, which includes NDs, MDs, PhDs, RDs, an MS, and an LAc, has summarized the essence of several of the most interesting studies.
This issue looks at various dietary factors and how they influence cardiometabolic health. Research summaries include: (1) blueberries for type 2 diabetes, (2) almonds for cardiovascular disease, (3) intermittent fasting and muscle mass, (4) sweet drinks and “sweet tooth,” and (5) stevia and appetite.
Blueberries provide cardiometabolic benefits in type 2 diabetes
Blueberries are a rich source of polyphenols, including anthocyanins, which have been associated with a reduced risk for developing type 2 diabetes. A recent double-blind, randomized, placebo-controlled trial evaluated the effects of daily consumption of blueberries on various cardiometabolic parameters in men with type 2 diabetes.
The study included 52 males (ages 51-75) who were overweight to morbidly obese (BMI 26-45) and had type 2 diabetes. All participants were taking diabetes medication other than insulin and many had typical comorbidities such as hypertension and dyslipidemia. For eight weeks, half of the participants ate 11 grams of blueberries (as freeze-dried powder in water; equivalent to one-half cup fresh) and half took a placebo powder twice daily (with breakfast and dinner).
Data was collected at baseline and trial end for height and weight (to calculate BMI), waist circumference, blood pressure, heart rate, serum cholesterol (total, HDL, LDL), triglycerides, high-sensitivity C-reactive protein, glucose, hemoglobin A1C (HbA1c), insulin, fructosamine, complete metabolic panel, and urine microalbumin-creatinine ratio.
HbA1c, fructosamine, triglycerides, and liver enzymes improved in the blueberry group versus the placebo group. Although cholesterol measures were not significantly different for the total cohort, they were significantly improved in the subgroup of blueberry-consuming participants who were taking lipid-lowering medications, which suggests a possible synergistic effect. The other measured parameters were not significantly changed in the study group compared to the placebo.
Contributed by Sheena Smith, MS MA
- Stote K, Wilson M, Hallenbeck D, et al. Effect of blueberry consumption on cardiometabolic health parameters in men with type 2 diabetes: an 8-week, double-blind, randomized, placebo-controlled trial. Curr Dev Nutr 2020;4(4). doi:10.1093/cdn/nzaa030
Does snacking on whole almonds decrease cardiovascular disease risk?
Almonds are a good source of protein, dietary fiber, unsaturated fatty acids, and other nutrients, and have been shown to reduce the risk of cardiovascular disease and type 2 diabetes and to decrease LDL cholesterol and fasting blood sugar. In this study, researchers investigated the effect of eating whole almonds, instead of popular snack foods, on cardiometabolic health.
Men and women (ages 30-70) with above average risk for developing cardiovascular disease were randomly assigned to one of two intervention groups: whole almonds as daily snacks or “control snacks,” which were sweet and savory mini-muffins formulated to be representative of average snacks.
The primary study outcomes included endothelial function and liver fat, while secondary study outcomes were blood glucose, insulin, lipid profile, adipokines, markers of fatty liver, body composition, blood pressure, heart rate variability, pancreatic and skeletal muscle fat, fecal short-chained fatty acids, plasma fatty acid profiles, and metabolomic profiles. Participants were tested on all study outcomes after a 2-week dietary lead-in with control snacks followed by six weeks of dietary intervention.
At study completion, participants in the almond snack group had significant improvements in endothelial function but no change in liver fat compared to the control snack group. LDL-cholesterol was significantly decreased in the almond snack group, while the remaining secondary outcome measures showed no differences between groups. The authors concluded that whole almonds as a replacement for typical snacks can have a significant impact on improving health and reducing cardiovascular disease risk by as much as 30 percent.
Contributed by Jennifer L. Greer, ND, MEd
- Dikariyanto V, Smith L, Francis L, et al. Snacking on whole almonds for six weeks improves endothelial function and lowers LDL cholesterol but does not affect liver fat and other cardiometabolic risk factors in healthy adults: the ATTIS study, a randomized controlled trial. Am J Clin Nutr 2020;nqaa100. doi:10.1093/ajcn/nqaa100
Time-restricted eating (intermittent fasting) can lead to loss of lean mass
Time-restricted eating (TRE), also referred to as intermittent fasting, has been increasingly promoted as a method to reduce weight and regulate metabolism. The basic idea is that, for a certain time period, eating normally alternates with either fasting or significantly reduced caloric intake. This might be five days of normal eating and two days of fasting, or an every-other-day pattern, or a daily regimen of eating only during set hours (often eight hours) and fasting the remaining hours. Although studies in animals have been encouraging, human studies have had mixed results and have generally not performed better than other methods of calorie restriction.1
This prospective, randomized trial – published in the Journal of the Endocrine Society – sought to better answer unresolved questions about TRE.2 Overweight or obese individuals (n=148) were enrolled in the 12-week study. Only 100 completed the trial – a relatively high dropout rate of 28.5 percent – which could have skewed findings. Individuals in the fasting group ate from noon until 8:00 pm (8 hours) and fasted the remaining 16 hours.
The control group ate three meals daily. For those who completed the trial, overall weight reduction was higher in the TRE group (-1.62 kg versus -0.57 kg). Unfortunately, loss of fat-free mass; i.e., loss of lean mass (muscle and possibly bone) seemed to account for the entire difference between the active and control arms.
This did not appear to have a negative impact on strength over the duration of the study. The authors noted no differences “in plasma ketones, insulin, or glucose between treatment groups.” Although some loss of lean body mass is to be expected with weight loss, over time it can lead to potentially negative effects for bone, muscle, strength, and metabolic health. Longer studies are needed to determine if this is a short-term phenomenon or a persistent problem.
Contributed by Jacqueline Jacques, ND
- Harris L, Hamilton S, Azevedo LB, et al. Intermittent fasting interventions for treatment of overweight and obesity in adults: a systematic review and meta-analysis. JBI Evid Synth 2018;16(2):507–547.
- Lowe D, Weiss E, Olgin J, et al. MON-LB107 Treat: A randomized controlled trial examining the effects of time restricted eating on weight loss and metabolic markers. J Endocr Soc 2020;4(Supp 1). doi:10.1210/jendso/bvaa046.2144
Effect of sweet drinks on satiety and sugar cravings
Consuming low-calorie sweeteners (LCS) compared to their sugar-sweetened counterparts clearly lowers total calorie consumption and reduces body weight. There is some concern that this creates a need for sweet flavors – the infamous “sweet tooth.” The researchers studied whether consumption of LCS beverages increased preference for sweet foods/beverages or whether this is a false assumption.
Sensory-specific satiety (SSS) is a perceived reduction in the pleasantness of taste and the desire to consume a food or flavor that occurs while eating. Essentially, the desire for a taste is satiated by consuming the flavor, which reduces the desire for more foods or drinks of that same taste.
Three separate studies were performed to assess whether SSS generalizes from sweet drinks to sweet foods. The aim of the studies was to determine if consumption of a sweet drink adequately decreased desire for sweet foods. Two of the studies used a two-condition, cross-over design and included 104 male and female participants.
The participants consumed water or non-carbonated fruit drinks sweetened with LCS and then evaluated various food and drink samples considered sweet or savory. Generalization of SSS was evident for all sweet food and drink samples, but did not have an effect on the savory food and drink samples. These effects were present when measured shortly after consumption but were not sustained when measured two hours later. No “rebound” effect was observed in the desire for sweet foods/drinks after the 2-hour window.
The third study included 51 participants and utilized a four-condition, cross-over design. Participants consumed labeled and branded cola, diet (LCS-sweetened) cola, still water, and carbonated water immediately before and during ad libitum consumption of sweet and non-sweet snack foods.
Compared with still water, the diet cola reduced sweet food intake but not total snack intake. Consumption of carbonated water decreased the sensation of hunger and increased reported fullness compared with still water, although it did not affect reported levels of thirst. Sugar-containing cola decreased overall snacking.
The data demonstrates that consuming LCS drinks acutely decreases the desire for sweet foods, dispels the assumption that sweet drinks promote a “sweet tooth,” and supports the use of LCS beverages in place of drinks sweetened with sugar. An unexpected outcome raised questions as to the importance of carbonation on overall satiety.
Contributed by Amanda Frick, ND, LAc
- Rogers P, Ferriday D, Irani B, et al. Sweet satiation: Acute effects of consumption of sweet drinks on appetite for and intake of sweet and non-sweet foods. Appetite 2020;149:104631. doi:10.1016/j.appet.2020.104631
Stevia prior to lunch decreases appetite and food intake without affecting blood sugar
A study of 20 healthy adults (average age 27) looked at the effect of five different beverages on appetite and blood sugar levels. The study consisted of participants taking one of five test beverages and then switching to another on each successive visit: (1) 330 mL water (control; no calories, no sweet taste); (2) 330 mL water with 40 grams of glucose (160 calories, sweet taste); (3) 330 mL of water with 40 grams of sucrose (160 calories, sweet taste); (4) 330 mL water with maltodextrin (160 calories, no sweet taste); or (5) 330 mL water with 240 ppm stevia (no calories, sweet taste).
Blood glucose levels and subjective appetite were measured at baseline (prior to beverage consumption) and then at 15, 30, and 60 minutes post-consumption. At 30 minutes, the participants were also offered a meal, during which they could eat as much as they wanted and food intakes were measured.
As would be expected, sucrose, glucose, and maltodextrin increased blood sugar, while water and stevia did not. In terms of appetite, caloric beverages (glucose, sucrose, and maltodextrin) and sweet beverages (glucose, sucrose, and stevia) all decreased subjective appetite compared to water.
In terms of caloric intake (beverage preload + meal), the beverage resulting in the lowest caloric intake was stevia, while there was no difference in caloric intake between water and the caloric beverages (meaning when drinking the water, the participant must have made up for no calories by eating more food). Stevia decreased appetite and subsequent food intake without raising blood glucose levels.
Contributed by Kathi Head, ND
- Stamataki N, Scott C, Elliott R, et al. Stevia beverage consumption prior to lunch reduces appetite and total energy intake without affecting glycemia or attentional bias to food cues: a double-blind randomized controlled trial in healthy adults. J Nutr 2020;150(5):1126-1134.