Around the world, there has been a sharp increase in the rates of insulin resistance and type 2 diabetes. In the United States, the Centers for Disease Control and Prevention (CDC) estimate that 29.1 million people have diabetes. That is approximately 9.3 percent of the population.
To treat existing diabetes, the CDC urge people to eat healthily, exercise regularly, and use medications that reduce blood glucose levels. They also emphasize the need to reduce cardiovascular disease risk factors, such as high blood pressure and high lipid levels, and to avoid tobacco use.
High LDL cholesterol associated with diabetes
CDC statistics indicate that between 2009-2012, 65 percent of people with diagnosed diabetes who were aged 18 years and above either had high levels of LDL, or "bad," cholesterol in the blood, or they were using drugs to lower cholesterol.
Amid urgent calls for new ways to prevent type 2 diabetes, some research has focused on how different carbohydrates and dietary fats impact metabolic health.
This has been controversial, and it has led to confusion regarding dietary guidelines and health priorities.
Senior author Dr. Dariush Mozaffarian, dean of the Friedman School of Nutrition Science and Policy at Tufts University in Medford, MA, and first author Fumiaki Imamura, of the Medical Research Council (MRC) Epidemiology Unit at the University of Cambridge, United Kingdom, led the meta-analysis.
'Don't fear healthy fats'
They looked at data for 4,660 adults that had been collected in 102 studies. In the randomized, controlled trials, the adults were given meals containing various types and quantities of carbohydrate and fat.
The researchers examined how these variations in diet impacted measures of metabolic health, and specifically, how saturated, monounsaturated and polyunsaturated fats and carbohydrates impact the development of type 2 diabetes.
The study focused on key biological markers of glucose and insulin control. These were blood sugar, blood insulin, insulin resistance and sensitivity, and how well the body was able to produce insulin in response to blood sugar.
Results suggested that consuming foods rich in monounsaturated fat or polyunsaturated fat had a positive effect on blood glucose control, compared with consumption of dietary carbohydrate or saturated fat.
For each 5 percent of dietary energy that was switched from carbohydrates or saturated fats to mono- or polyunsaturated fats, they found a drop of around 0.1 percent in HbA1c - a blood marker of long-term glucose control.
Previous research has suggested that for each 0.1 percent decrease in HbA1c, the incidence of type 2 diabetes drops by 22 percent and the chance of developing cardiovascular diseases falls by 6.8 percent.
Imamura notes that replacing carbohydrates and saturated fats with polyunsaturated fats appears to be consistently beneficial.
Imamura adds: "This is a positive message for the public. Don't fear healthy fats."
"The world faces an epidemic of insulin resistance and diabetes. 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."
Dr. Dariush Mozaffarian
This is the first time a team has systematically reviewed all the available evidence measuring the effects of carbohydrate and different kinds of fat in the diet.
The authors hope that the results will help scientists, healthcare workers, and the public to set priorities that will help to combat the worldwide problem of type 2 diabetes.
Effects of saturated fat, polyunsaturated fat, monounsaturated fat, and carbohydrate on glucose-insulin homeostasis: A systematic review and meta-analysis of randomised controlled feeding trials., Fumiaki Imamura et al., PLOS Medicine, doi:10.1371/journal.pmed.1002087, published online 19 July 2016.
Tufts University news release, accessed 18 July 2016 via EurekAlert.
Additional source: CDC, National Diabetes Statistics Report 2014, accessed 18 July 2016.