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One of the most pronounced health disparities in the United States may also be one of the most visible: Black women are more likely than any other segment of the population to be obese. According to the Centers for Disease Control and Prevention, 38 percent of European Americans, male and female, are obese. The rate is 37 percent for African American men. For African American women, it is 55 percent.
During the past two decades, Barbara Gower, Ph.D., professor and vice chair for Research in the Department of Nutrition Sciences, has been investigating the causes of this disparity. Gower is in the middle of a five-year, $1.9 million study testing her hypothesis that Black women are more prone to obesity because of three separate factors. High insulin secretion and high insulin sensitivity set the stage, she argues — and when you combine that with a high-sugar diet, excess weight becomes locked in. But Gower’s study is testing a solution: a low-sugar diet that overcomes insulin issues and a lifetime of weight struggles.
“Something insulin does really well is build fat stores — that’s where it excels.” The good news: “Insulin is secreted only in response to sugar,” Gower said. “If you eat a lot of sugar, you will secrete a lot of insulin.”
Disparities related to insulin
Gower’s work is focused on a physiological disparity related to insulin. Insulin is “a builder hormone” that signals muscle and fat cells to take fuel out of the bloodstream and store it, Gower explained. “Something insulin does really well is build fat stores — that’s where it excels,” she said.
“I started in this area about 20 years ago, studying 7-year-olds,” Gower said. “We would do glucose tolerance tests, where everyone drinks glucose, which is sugar, in identical amounts. The kids were a mix of overweight and lean; but the insulin levels were twice as high in the Black children, even taking into account body weight.”
Multiple other studies by Gower confirmed this finding and added others: African Americans not only secrete more insulin, but they also clear less of it. That leaves a high amount of insulin in the bloodstream after a meal, which signals the body to store fat. In the context of a diet high in sugar, which causes insulin levels to spike, individuals with high insulin secretion and low clearance will turn more food to fat than individuals with lower insulin secretion and higher insulin clearance. “I looked at 20 years of data, and it all supported this,” Gower said.
Low-glycemic diets under study
The situation is not hopeless, Gower says. While there is not much a person can do about innate insulin secretion, clearance and sensitivity, diet is very much under our conscious control.
“Insulin is secreted only in response to sugar,” Gower said. “If you eat a lot of sugar, you will secrete a lot of insulin.”
But if you eat carefully, Gower’s studies show, you can avoid this pitfall. Her work has pointed to a solution: diets low in sugary foods. Such “low glycemic” diets limit the flood of glucose into the bloodstream.
“If you have elevated insulin, these diets work like magic,” Gower said. “You will lose the weight, and importantly, you should be able to keep it off.”
To bear out these early observations, Gower received funding from the National Institute of Diabetes and Digestive and Kidney Diseases for a larger trial, which is ongoing.
Participants — all African American women — have their insulin levels measured on entrance to the study and then are randomized to either a low-glycemic or a high-glycemic diet.
Barbara Gower, Ph.D. (Photography: Lexi Coon)How the study works
“We’re feeding participants the same number of calories — 60 percent of their estimated energy requirements,” she said. “First we figure out what they burn: Say it’s 2,000 calories. If they are eating 60 percent of that, they should lose weight. We are then looking to determine who is more successful with keeping the weight off, considering insulin level and diet assignment. The results from this study will lead to a personalized medicine approach to weight management, allowing health care providers to match someone’s insulin level to the diet that is right for them.”
The work has implications for many different populations, Gower notes.
“There are people with high insulin who are not Black,” she said. “There was a study in England a few years ago of people with a family history of Type 2 diabetes. They found exactly the same thing: The people with the highest insulin sensitivity and secretion were fighting weight problems their whole lives. Anyone with a family history of diabetes, the stocky kids in school — that’s how they are wired.
“These are the people who need a low-glycemic diet,” Gower said. It does not have to be low-carb, but the foods have to be selected to minimize a rapid increase in blood sugar, she says.
“Things you know you shouldn’t be eating: sugar-sweetened beverages and highly processed foods, for example. We’re always told you have to count calories, but it matters what you eat.”
Women interested in joining the study can complete an online screening form here.