By Joseph E. Scherger, MD, MPH

Vice President, Primary Care, Eisenhower Medical Center; Clinical Professor, Keck School of Medicine, University of Southern California, Los Angeles

Dr. Scherger reports no financial relationships relevant to this field of study.

SYNOPSIS: Once obese, a patient’s metabolism adapts with insulin resistance to maintain body fat. High insulin levels promote fat storage and block fat burning.

SOURCE: Jung SH, Jung CH, Reaven GM, Kim SH. Adapting to insulin resistance in obesity: Role of insulin secretion and clearance. Diabetologia 2017 Dec 1. doi: 10.1007/s00125-017-4511-0. [Epub ahead of print].

Jung et al studied insulin metabolism in 91 obese patients without diabetes to show/learn/identify how insulin resistance develops and results in the continued deposition and storage of fat. These investigators from Stanford and South Korea studied the patients’ responses to an oral glucose tolerance test. Both insulin resistance and insulin clearance were measured. Over time, patients develop and maintain insulin resistance. In a previous study, investigators showed how plasma insulin concentration and insulin resistance increases steadily in obese patients.¹

COMMENTARY

Jason Fung, MD, is a nephrologist who studies obesity management. He directs the Intensive Dietary Management Program at the University of Toronto. In his 2016 book, The Obesity Code: Unlocking the Secrets of Weight Loss, Fung systematically explained why obesity should be considered a hormonal problem, noting that the central hormone is insulin.² In medical school, clinicians learned that insulin works by driving glucose into cells. In people with type 1 diabetes, that central role for insulin is critical. However, patients with type 2 diabetes have an abundance of insulin, and insulin resistance develops. Another central role for insulin is as a fat-storage hormone. When patients consume more carbohydrates than they need for energy stores, insulin stimulates lipogenesis. Repeated spikes in insulin levels from heavy carbohydrate consumption results in insulin resistance. Fung described how high insulin levels block the burning of fat and, hence, how insulin becomes the central fat storage hormone. The research articles cited here support this claim. I have started measuring fasting insulin levels with my routine labs. The normal range for fasting insulin is lab dependent but generally includes a wide range, such as 2.5-26, a reflection of fasting insulin levels in the general population. Fung reported the research showing that fat burning and weight loss do not occur unless fasting insulin levels are below 10. The most efficient way to achieve this is by intermittent fasting. Twelve hours of fasting may be enough to lower insulin levels in normal-weight patients, but in obese patients with insulin resistance, 16- to 24-hour fasts may be necessary. Fung even uses multiday fasts in his clinic. Most programs for treating obesity focus on what we eat, and, currently, reduced glycemic load (low carbohydrates) is in favor. Carbohydrates drive hunger with fluctuating glucose and insulin levels. Over time, both glucose and insulin levels remain elevated. Fasting is a great way to reset this metabolic system and facilitate the burning of fat for weight loss.

REFERENCES

1. Kim MK, Reaven GM, Kim SH. Dissecting the relationship between obesity and hyperinsulinemia: Role of insulin secretion and insulin clearance. Obesity (Silver Spring) 2017;25:378-383.
2. Fung J. The Obesity Code: Unlocking the Secrets of Weight Loss. Vancouver BC: Greystone Books; 2016.