Despite similar weight loss, low-carbohydrate diet delivers insulin reductions, smaller fat cells than low-fat diet
LOS ANGELES — Eating plans low in carbohydrates result in smaller fat cells vs. low-fat/higher-carbohydrate plans after similar weight loss, which may yield better metabolic health, according to a speaker at the World Congress of Insulin Resistance, Diabetes and Cardiovascular Disease.
“It’s pretty clear that when you have a lot of smaller fat cells, your metabolic health is tremendously improved,” Tracey McLaughlin, MD, MS, professor of medicine, endocrinology, gerontology and metabolism at the Stanford University Medical Center, said during her presentation. “As the fat cells get bigger, they predict the development of diabetes.”
In a study assessing the effects of weight loss on cardiovascular risk factors among adults with insulin resistance and overweight, but not obesity, McLaughlin and colleagues found that a modest weight loss of roughly 5 kg significantly improved insulin resistance, and that improvement was associated with adipose cell size.
“Fat cell size appears to be an even stronger predictor of insulin resistance than obesity per se,” McLaughlin said. “[In the study], the more weight you lost, the more [insulin action] improved; but the more your fat cell size shrank, the more your insulin action improved.”
Diet studies that manipulate the macronutrient content of eating plans demonstrate that weight loss depends on calorie restriction, McLaughlin said. Participants who comply with the plan, whether low carbohydrate or low-fat/higher carbohydrate, experience weight loss. However, weight loss alone may not result in improved insulin resistance.
“You can lose weight, but if you’re having a lot of carbs and your insulin is sky high, maybe your fat cells aren’t shrinking as much,” McLaughlin said.
In a substudy of the DIETFITS trial, McLaughlin and colleagues obtained fat biopsies from 40 participants at baseline and at 6 months of demonstrated compliance with either a healthy low-fat (n = 21; 20 g fat per day) or healthy low-carbohydrate diet (n = 19; 20 g per day increased by 5 g per day over several weeks). Weight loss and BMI were similar between the groups. At 6 months, the researchers took fat biopsies from participants before a meal tolerance test and 2 hours later, when insulin level peaked.
Insulin levels remained very low, less than 50 µU/mL, for the low-carb diet group, whereas the low-fat diet group had higher insulin levels that peaked above 350 µU/mL. Circulating fatty acids were higher and lipolysis greater among the low-carb group.
In addition, the low-carb diet group demonstrated a reduction from baseline in the size of their fat cells, whereas there was no change in adipose cell size among the low-fat diet group.
“When you separate the correlation of the change in weight and change in fat cell size — because as you lose weight, your cells should shrink — you can see that this is apparent only in the low-carb group,” McLaughlin said. “The more weight they lost, the more their cells shrank, and this effect was mitigated in the low-fat/high-carb group.”
McLaughlin said further studies are needed to determine whether the shrinking of adipose cells translates into better health benefits with a low-carb vs. low-fat diet.
McLaughlin TL. Effect of very low carb vs. very low fat diet on adipose tissue and FFA metabolism. Presented at: World Congress on Insulin Resistance, Diabetes and Cardiovascular Disease; Dec. 4-7, 2019; Los Angeles.
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