Field Notes
Healthful Fats May Help Prevent Type 2 Diabetes
Eating more unsaturated fats, especially polyunsaturated fats, in place of either dietary carbohydrate or saturated fats lowers blood sugar levels and improves insulin resistance and secretion, according to a new meta-analysis of data from 102 randomized controlled feeding trials in adults.
The study, led by Dariush Mozaffarian, MD, DrPH, dean of the Friedman School of Nutrition Science and Policy at Tufts University, and Fumiaki Imamura, PhD, of the Medical Research Council Epidemiology Unit at the University of Cambridge, provides novel quantitative evidence for the effects of dietary fats and carbohydrate on the regulation of glucose and insulin levels and several other metrics linked to type 2 diabetes.
The results were published in PLOS Medicine.
Rates of insulin resistance and type 2 diabetes are rising sharply worldwide, highlighting the need for new, evidence-based preventive strategies. While a healthful diet is clearly a cornerstone of such efforts, the effects of different dietary fats and carbohydrate on metabolic health have been controversial, leading to confusion about specific dietary guidelines and priorities.
“The world faces an epidemic of insulin resistance and diabetes,” says Mozaffarian, senior author on the study. “Our findings support preventing and treating these diseases by eating more fat-rich foods like walnuts, sunflower seeds, soybeans, flaxseed, fish, and other vegetable oils and spreads, in place of refined grains, starches, sugars, and animal fats.
“This is a positive message for the public: Don’t fear healthy fats,” he adds.
In their study, Imamura, Mozaffarian, and colleagues performed the first systematic evaluation of all available evidence from trials to quantify the effects of different types of dietary fat (eg, saturated, monounsaturated, and polyunsaturated) and carbohydrate on key biological markers of glucose and insulin control that are linked to development of type 2 diabetes.
The team identified and summarized findings from 102 randomized controlled trials, involving a total of 4,660 adult participants, who were provided meals that varied in the types and amounts of fat and carbohydrate. The team then evaluated how such variations in diet affected measures of metabolic health, including blood sugar, blood insulin, insulin resistance and sensitivity, and ability to produce insulin in response to blood sugar.
The researchers found that exchanging dietary carbohydrate or saturated fat with a diet rich in monounsaturated fat or polyunsaturated fat had a beneficial effect on key markers of blood glucose control. For example, for each 5% of dietary energy switched from carbohydrates or saturated fats to mono- or polyunsaturated fats, there’s an approximately 0.1% reduction in HbA1c. The authors note that based on previous research, each 0.1% reduction in HbA1c is estimated to reduce the incidence of type 2 diabetes by 22% and cardiovascular diseases by 6.8%.
“Among different fats, the most consistent benefits were seen for increasing polyunsaturated fats, in place of either carbohydrates or saturated fat,” says Imamura, first author on the study.
Given the current global pandemic of type 2 diabetes, the authors hope that these findings will help inform scientists, clinicians, and the public on dietary priorities related to dietary fats and carbohydrates and metabolic health.
“Until now, our understanding of how dietary fats and carbohydrate influence glucose, insulin, and related risk factors has been based on individual studies with inconsistent findings,” Imamura says. “By combining results from more than 100 trials, we provide the strongest evidence to date on how major nutrients alter these risks.”
— Source: Tufts University
Ordering Food Early Could Reduce Calories
Want to cut calories and make more healthful meal choices? Try avoiding unhealthful impulse purchases by ordering meals at least an hour before eating. New findings from researchers at the Perelman School of Medicine at the University of Pennsylvania and Carnegie Mellon University show that people choose higher-calorie meals when ordering immediately before eating, and lower-calorie meals when orders are placed an hour or more in advance. The results, which have implications for addressing the nation’s obesity epidemic, are published in the Journal of Marketing Research.
“Our results show that ordering meals when you’re already hungry and ready to eat leads to an overall increase in the number of calories ordered, and suggest that by ordering meals in advance, the likelihood of making indulgent purchases is drastically reduced,” according to lead author Eric M. VanEpps, PhD, a postdoctoral researcher at the Penn Center for Health Incentives and Behavioral Economics, who conducted the studies while a graduate student at Carnegie Mellon. “The implication is that restaurants and other food providers can generate health benefits for their customers by offering the opportunity to place advance orders.”
Researchers conducted two field studies examining online lunch orders of 690 employees using an onsite corporate cafeteria, and a third study with 195 university students selecting among catered lunch options. Across all three studies, the researchers noted that meals with higher calorie content were ordered and consumed when there were shorter (or no) waiting periods between ordering and eating.
The first study was a secondary data analysis of more than 1,000 orders that could be placed any time after 7 AM to be picked up between 11 AM and 2 PM. The second study randomly assigned participants to place orders before 10 AM or after 11 AM. The third study randomly assigned university students to order lunch before or after class, with lunches provided immediately after class.
In the first study, VanEpps and colleagues from Carnegie Mellon University found that for every hour of delay between when the order was placed and the food was ready (average delay of 105 minutes), there was a decrease of approximately 38 kcal in the items ordered. In the second study, the researchers found that those who placed orders in advance, with an average delay of 168 minutes, had an average reduction of 30 kcal (568 vs 598) compared with those who ordered closer to lunchtime (with an average delay of 42 minutes between ordering and eating). The third study showed that students who placed orders in advance ordered significantly fewer calories (an average of 890 kcal) compared with those who ordered at lunchtime (an average of 999 kcal).
In all three studies, lower caloric totals generally weren’t confined to any specific population subsets. Failure to eat breakfast didn’t emerge as a factor in the observed effect of time delay on total lunch calories, nor were there any observed differences in meal satisfaction between meals ordered in advance and those ordered for immediate consumption.
“These findings provide one more piece of evidence that decisions made in the heat of the moment are not as farsighted as those made in advance,” says George Loewenstein, PhD, the Herbert A. Simon Professor of Economics and Psychology at Carnegie Mellon, and senior author on the study. “For example, people who plan to practice safe sex often fail to do so when caught up in the act, and people who, in dispassionate moments, recognize the stupidity of road rage nevertheless regularly succumb to it. Unfortunately, precommitment strategies are more feasible when it comes to diet than to many other ‘hot’ behaviors.”
Based on findings from other studies, VanEpps says there’s a potential concern that people who cut calories in one meal might “make up” for the calorie reductions later, whether at dinner or via snacking, though there’s little evidence that participants in these studies were aware that lunches ordered in advance had fewer calories. The authors suggest future research in the form of longitudinal studies that measure eating decisions over a longer period of time would be useful in addressing this issue. In addition, because the two employee workplace studies provided discounted food and the university-based study provided free food, future research examining analogous situations where participants pay full price for their meals would be beneficial.
— Source: Perelman School of Medicine at the University of Pennsylvania