The glycemic index ranks carbohydrates from zero (foods with no glucose at all) to 100 (sweets and drinks that contain nothing but glucose). Simple carbohydrates that have more glucose are digested rapidly, causing dramatic spikes and crashes in blood sugar levels. Complex carbohydrates with less glucose are digested more slowly and help maintain steadier blood sugar levels throughout the day. All the people in the new clinical trial had coronary artery disease, which happens when plaque accumulation causes the heart’s major blood vessels to narrow and stiffen, limiting blood flow. Participants were also overweight or obese at the start of the trial, a risk factor for serious coronary artery disease complications like heart failure and heart attacks. During the three-month trial, researchers randomly assigned 160 adults to either switch to a low-glycemic-index diet or join a control group following a diet typically recommended for people with heart disease. In the control group, people were asked to limit fat and some proteins, such as whole milk, cheese, meat, egg yolks, and fried foods. No changes to fat or protein consumption were required for the low-glycemic-index diet group. With the low-glycemic-index diet, participants’ average body mass index (BMI) declined by 3.6 points, from 29.8 to 26.2. In the control group, the average BMI declined by 1.4 points, from 30.2 to 28.8. A BMI of 30 or more is considered obese, while a BMI of 25.0 to 29.9 is considered overweight. In addition, people on the low-glycemic-index diet reduced their waist circumference by an average of 9 centimeters (3.5 inches), compared with an average 3.3 centimeter (1.3 inch) reduction for the control group. “While larger studies are needed to confirm these findings, our research indicates that emphasizing low-glycemic-index foods as part of a balanced diet could help patients with heart disease control their body weight and their waistline,” says study co-author Jamol Uzokov, of the Republican Specialized Scientific Practical Medical Center of Therapy and Medical Rehabilitation in Tashkent, Uzbekistan. The results were presented at the ACNAP–EuroHeartCare Congress 2022, a scientific congress of the European Society of Cardiology. The study hasn’t been published in a peer-reviewed medical journal, a process that involves independent verification of the findings. One limitation of the analysis is that it relied on participants to accurately recall and report what they ate using food frequency questionnaires, a process that doesn’t always reflect true eating habits.
Low-Glycemic-Index Foods
Low-glycemic-index foods have a score of 50 or less, while foods considered high on this index tend to have a score over 70, according to the Cleveland Clinic. Low-glycemic-index foods include:
Vegetables (peppers, broccoli, tomatoes, lettuce, and eggplant)Fruits (strawberries, apples, and pears)Legumes (chickpeas, dried or boiled beans, and legumes)Dairy (whole milk and plain yogurt)Some sweets (like dark chocolate with more than 70 percent cocoa)Nuts (cashews and peanuts)
Many heavily processed foods can be higher on the glycemic index, according to the Cleveland Clinic:
Processed foods (corn chips and pretzels)Sugar-containing beverages (soda, sweet tea, and sports drinks)Fast food (cheeseburgers, fried chicken, and pizza)Baked goods (doughnuts, white bread, and cereals, unless they are whole grain)Potatoes (mashed potatoes and French fries)
Preparation also matters, since how foods are made can influence where they land on the glycemic index, the Cleveland Clinic notes. With oatmeal, for example, the instant packets you can make in the microwave could have a glycemic index score of 79, while the steel-cut oats cooked on the stove may have a glycemic index score of 55.
How Low-Glycemic-Index Foods Impact Heart Health
While the new study wasn’t designed to prove whether or how a low-glycemic-index diet might directly help prevent heart disease or minimize the risk of complications, it’s possible to reduce these outcomes by maintaining a healthy body weight and waist size, Uzokov says. That’s because obesity is one of the biggest risk factors for coronary artery disease, along with related health issues like type 2 diabetes, high cholesterol, and elevated blood pressure. It’s possible that study participants who followed the low-glycemic-index diet consumed fewer total calories and ate higher quality, nutrient-dense carbohydrates, aiding weight loss, says Carol Kirkpatrick, PhD, an associate professor and director of the Wellness Center at Idaho State University in Pocatello. “Typically, waist circumference will improve overall with weight loss regardless of the method of losing weight,” says Dr. Kirkpatrick, who wasn’t involved in the new study. Previous research has linked a high-glycemic-index diet to an increased risk of premature death from all causes and from cardiovascular disease in particular. One study published in April 2021 in The New England Journal of Medicine (NEJM) looked at eating habits for 137,851 people 35 to 70 years old, then followed them for about a decade. Compared with people with the lowest glycemic-index diet, participants with heart disease with the highest glycemic index diets were 51 percent more likely to experience or die from major cardiovascular disease events like heart attacks or strokes. A study published in March 2019 in Mayo Clinic Proceedings: Innovations, Quality & Outcomes found that each 10-point increase in the average glycemic index level of participants’ diets was associated with a 24 percent higher risk of developing coronary heart disease. When it comes to heart health, one main advantage of a low-glycemic-index diet is that it promotes consumption of nutrient-rich carbohydrates, a pitch that may be more appealing to patients than being told to abandon carbs altogether, says David Jenkins, MD, PhD, lead author of the NEJM study and a professor of nutrition sciences and medicine at the University of Toronto. A plant-based diet can provide a wide range of nutrients that promote heart health, and the fruits and vegetables that make up part of a heart-healthy diet can also contain lots of carbohydrates, says Dr. Jenkins, who wasn’t involved in the latest study. Following a low-glycemic-index diet encourages people to consume healthier carbohydrates like legumes and leafy greens and limit their intake of super sugary foods with little nutritional value, he notes. “A low-glycemic-index diet encourages you to consume a balanced, healthy diet including beneficial carbohydrates,” Jenkins says. “Eating this way can help maintain a healthy body weight and a healthy body shape, and it can prevent obesity — one of leading risk factors for heart disease.”
