HOW DOES INSULIN AFFECT WEIGHT LOSS?
When you hear the word insulin, you might think it only matters if you have diabetes. That makes sense — the two are intimately linked. Insulin, known as the storage hormone for its role in shuttling blood sugar into your cells, plays a key role in both type 1 and type 2 diabetes, according to the Cleveland Clinic.
But insulin can also be a factor when you’re trying to lose weight or maintain a healthy weight. After all, people who take insulin tend to gain weight, according to the Mayo Clinic. So it stands to reason you don’t want too much of the stuff floating around your bloodstream. Should insulin levels be a concern for people who don’t have diabetes? We asked registered dietitians to set the record straight on what healthy people need to know about insulin and weight loss.
What Is Insulin?
According to the Cleveland Clinic, insulin is a hormone that is made in the pancreas. Insulin acts like a key that opens the doors to your cells so glucose can enter. It helps your body use glucose, a kind of sugar that is your body’s main energy source, to power your everyday activities. In healthy people, when blood sugar rises after eating, insulin levels rise just enough to help move that glucose into your cells, where it can be used for fuel.
In people with diabetes, this interplay between blood sugar and insulin gets disrupted. With type 1 diabetes, the problem is a lack of insulin due to an autoimmune disease that destroys the pancreas’ ability to make insulin. With type 2 diabetes, the pancreas is pumping out insulin, but the body’s cells stop responding to it, a condition called insulin resistance. It’s as if the keys don’t work anymore, so the pancreas makes even more insulin, leading to elevated levels of insulin and too much blood sugar.
How Does Insulin Affect Weight?
If you’re healthy — no diabetes or insulin resistance — insulin will work the way it’s supposed to. “For anyone with normal-functioning insulin responses, weight gain is less about your insulin levels and more about eating more than your body needs,” says Jordan Hill, RD, owner of Hill Health Nutrition in Denver, Colorado.
It’s when you don’t have a normal insulin response that insulin becomes a weight issue. “Insulin resistance presents a crucial turning point,” says Kelsey Costa, RDN, a nutrition consultant for Diabetes Strong in Boston. “It's a condition that can emerge even before overt diabetes develops, acting as an early warning signal for potential health issues ahead.” The signs of insulin resistance include elevated fasting blood sugar levels (over 100 mg/DL), increased waist circumference, and high blood pressure, says Costa.
Insulin resistance triggers the pancreas to make more insulin, hiking up the amount of insulin in the bloodstream, according to the National Institute of Diabetes and Digestive and Kidney Diseases.
Elevated insulin levels disregulate hunger and fullness signals, according to a research review published in the Canadian Journal of Diabetes. It can also inhibit the breakdown of stored fat, according to a review published in the American Journal of Physiology. In a nutshell, too much insulin can lead you to eat more and gain weight. Insulin resistance is very common — one in three American adults is insulin resistant, according to Standford Medicine. Luckily, with health lifestyle changes it is possible to reverse insulin resistance, according to Cleveland Clinic.
The flip side of insulin resistance is insulin sensitivity. You want your cells to be sensitive to insulin’s effects. “High insulin sensitivity means that cells require lower levels of insulin to uptake glucose efficiently, which is a beneficial thing,” says Hill. Insulin sensitivity is your best defense against insulin resistance, according to the Cleveland Clinic.
Expert Advice for Healthy Insulin Levels
Good habits can help keep your blood glucose, insulin levels, and weight in check according to the Centers for Disease Control and Prevention. Diet is top of the list of these lifestyle levers, but there is some debate about exactly what eating strategy is best.
Keto
There has been some evidence that following the ketogenic diet, an ultra-low-carb plan, may help improve insulin sensitivity. One systematic review and meta-analysis published in Nutrients looked at the effects in people who were either overweight or obese or had type 2 diabetes and concluded that “ketogenic diets improve insulin sensitivity through their irrefutable effects on fat and weight loss.” The authors noted that these results appear to not only be the result of weight loss, but also direct insulin-sensitizing effects caused by restricting carbohydrates to lower blood glucose and insulin levels. A separate systematic review and meta-analysis published in the journal Nutrition & Diabetes similarly found that keto diet appears to favorably impact fasting blood glucose and insulin levels as well as body weight results in people with type 2 diabetes. In both papers, however, the authors note the need for additional research in both diabetic and nondiabetic populations. The keto diet has been criticized as difficul to stick to, and less effective as a longterm solution, notes Hill. Costa says she can’t recommend the keto diet either. “It cuts out too many healthy, plant-based foods, and there’s a risk of vitamin and mineral deficiencies.”
Intermittent fasting
Intermittent fasting or IF is another approach people try to manage blood sugar and insulin through diet. The practice, which requires limiting your daily eating window to anywhere between 12 and 2 hours, appears to have some benefits. A study published in Nature Medicine found that IF resulted in greater insulin sensitivity and better post-meal blood glucose levels compared to caloric restriction or other methods. Separately, another systematic review and meta-analysis published in the journal Physiology & Behavior indicates that intermittent fasting in conjunction with resistance training may have favorable impacts on reducing total body weight, fat mass, and fat percentage while preserving muscle mass, says Hill. Still, the evidence supporting intermittent fasting for insulin levels is far from overwhelming. “It’s an ongoing topic of research, Hill says. “For anyone considering implementing intermittent fasting, I recommend meeting with a registered dietitian to determine if it’s appropriate for you.”
Commonsense strategies
It’s tempting to try something trendy like keto or intermittent fasting to speed up weight loss, manage blood glucose, and improve insulin sensitivity. But the experts recommend more tried-and-true ways to accomplish these goals. Here are Costa and Hill’s best science-backed tips for regulating insulin and losing weight:
- Adopt a Mediterranean-style diet. A study published in the journal Nutrients found that this style of eating, which emphasizes plant-based foods and healthy fats, improved insulin sensitivity in overweight and obese people without diabetes.
- Cut added sugars. A narrative review of the research published in the journal Nutrients suggests that added sugars contribute to insulin resistance.
- Add protein to meals and snacks. One study in the journal Nutrients found that a high-protein diet was even more effective than a Mediterranean diet for improving insulin sensitivity.
- Choose unsaturated fats. Research published in the journal Lipids in Health and Disease notes that “higher levels of unsaturated fat in the diet may be a protective factor associated with a lower risk of developing insulin resistance.”
- Eat plenty of fiber. Fiber improves insulin resistance according to research published in the journal Nutrients. That’s one reason why the Academy of Nutrition and Dietetics recommends that women eat 25 grams of fiber per day and men should get 38 grams. But Americans eat only 10 to 15 grams of fiber each day, according to Harvard Medical School. So if you’re like most people, eating more fiber is a big opportunity to upgrade your health.
- Don’t overlook physical activity. According to the American Diabetes Association, exercise, even a walk after dinner, is one of the best ways to improve insulin sensitivity. The best news is that the benefits start right after your next workout — physical activity improves insulin sensitivity for the next 24 hours.
- Sleep matters. Researchers found that sleeping less than 6.2 hours per night led to a 14.8 percent increase in insulin resistance in a study published in the journal Diabetes Care. The American Academy of Sleep Medicine recommends at least seven hours of sleep each night.
If you don’t have diabetes or insulin resistance, insulin shouldn’t be a major concern on your weight loss journey. An annual checkup can reveal your fasting glucose numbers and whether you’re prediabetic or flirting with insulin resistance. Even if you aren’t, it’s always smart to follow a balanced eating plan and stay active to keep blood sugar on an even keel and promote overall well-being and weight loss.
Editorial Resources and Fact-Checking
- Insulin. Cleveland Clinic. January 17, 2024.
- Insulin and weight gain: Keep the pounds off. Mayo Clinic. September 1, 2022.
- Insulin Resistance & Prediabetes. National Institute of Diabetes and Digestive and Kidney Diseases. May 18, 2018..
- Insulin Resistance. Cleveland Clinic. December 16, 2021.
- Insulin resistance doubles risk of major depressive disorder, Stanford study finds. Stanford Medicine. September 22, 2021.
- Healthy Weight. Centers for Disease Control and Prevention. December 30, 2022.
- Yuan X et al. Effect of the ketogenic diet on glycemic control, insulin resistance, and lipid metabolism in patients with T2DM: a systematic review and meta-analysis. Nutrition & Diabetes. November 30, 2020.
- Intermittent fasting for weight loss in people with type 2 diabetes. National Institutes Health. November 7, 2023.
- Ashtary-Larky D et al. Effects of intermittent fasting combined with resistance training on body composition: a systematic review and meta‐analysis. Physiology & Behavior. August 1, 2021
- Sood S et al. Higher Adherence to a Mediterranean Diet Is Associated with Improved Insulin Sensitivity and Selected Markers of Inflammation in Individuals Who Are Overweight and Obese without Diabetes. Nutrients. October 21, 2022.
- Gillespie K et al. The Impact of Free Sugar on Human Health — A Narrative Review. Nutrients. February 10, 2023.
- Conde S et al. A High Protein Diet Is More Effective in Improving Insulin Resistance and Glycemic Variability Compared to a Mediterranean Diet — A Cross-Over Controlled Inpatient Dietary Study. Nutrients. December 7, 2021.
- Chen X et al. High dietary intake of unsaturated fatty acids is associated with improved insulin resistance – a cross-sectional study based on the NHANES database. Lipids in Health and Disease. December 5, 2023.
- Niero M et al. Impact of Dietary Fiber on Inflammation and Insulin Resistance in Older Patients: A Narrative Review. Nutrients. May 18, 2023.
- Easy Ways to Boost Fiber in Your Daily Diet. Academy of Nutrition and Dietetics. March 1, 2021.
- Should I be eating more fiber? Harvard Health Publishing. February 27, 2019.
- Blood Glucose and Exercise. American Diabetes Association.
- Zuraikat F et al. Chronic Insufficient Sleep in Women Impairs Insulin Sensitivity Independent of Adiposity Changes: Results of a Randomized Trial. Diabetes Care. November 13, 2023.
- Teong Tong X et al. Intermittent fasting plus early time-restricted eating versus calorie restriction and standard care in adults at risk of type 2 diabetes: a randomized controlled trial. Nature Medicine. April 6, 2023.
- Paoli A et al. The Effects of Ketogenic Diet on Insulin Sensitivity and Weight Loss, Which Came First: The Chicken or the Egg? Nutrients. July 12, 2023.
- Seven or more hours of sleep per night: A health necessity for adults. American Academy of Sleep Medicine. June 1, 2015