Low Carbohydrate Diets the Future for Weight Loss in Obesity 

Is a very low carbohydrate diet (VLCD) superior to an essential carbohydrate/low-fat diet (LFD) for improving body mass and insulin sensitivity? 

Many Americans suffer from overweight or obesity, and there is a high risk of cardio-metabolic disease seen in older adults with obesity. Many different diets are recommended by health care professionals, dieticians, and nutritionists to control weight loss. One standard diet is a very low carbohydrate diet (VLCD). Insulin resistance and buildup of visceral adipose tissue (VAT) and intermuscular adipose tissue (IMAT) hinder older adults with obesity. The purpose of this study was to evaluate older adults with obesity to identify if a VLCD generates a much more significant decrease of fat, conserves lean mass, and improves insulin sensitivity as compared to an essential carbohydrate/low-fat diet (LFD). Past studies state that weight loss with a caloric restriction decreases the resting metabolic rate and causes losses in lean tissue, leading to declining physical function in aging adults. Other studies recommend changing the diet quality to improve weight loss while preventing the loss of skeletal tissues.  Previous studies measuring the insulin sensitivity reported that VLCD resulted in much lower insulin resistance and improved insulin sensitivity.  

The study was a randomized control trial, with two-arm (VLCD group and LFD group), parallel intervention. The EatRight Clinic determined the eligibility for the participants. The following devices were used to take measurements:  Dual-energy X-ray absorptiometry (DXA), Magnetic Resonance Imaging (MRI), fasting blood drawing, and the euglycemic-hyperinsulinemic clamps. The study was for 8 weeks, following a prescription diet. Participants were not blinded, but the study evaluators and testers were blinded. The VLCD group obtained ≤ 10% carbohydrates, 25% protein, and ≥ 65% fat.  The diet consisted of low glycemic options of carbohydrates, whole foods, leafy greens, non-starchy vegetables, fruits, and grains high in fiber—sources of fat from nut oils, butter, cheese, and avocados. The diet of patients in the LFD group was low-fat, with 55% carbohydrate, 25% protein, and 20% from fat, and included lean meats, with a low-fat dairy and whole grains, fruits, and vegetables. The VLCD group received two dozen eggs each week while the LFD received breakfast bars. 

A two-sided statistical analysis test was performed with alpha at 0.05 to determine statistical significance. The paired t-tests determined the difference in baseline and the post-intervention body composition, fat distribution, insulin sensitivity, and serum analysis. The covariance (ANCOVA) showed how diet is seen in baseline measurement after the intervention.   

The study was completed by 19 participants, women & men, in the VLCD group and 15 in the LFD.  The average age of the participants was 67-72, a diverse population. The VLCD group reported the greatest weight loss compared to the LFD group (-6.3% vs -1.0%; P-value < 0.001). Weight, total fat mass, VAT, SAAT, Thigh-SAT, Thigh, IMAT, and total lean mass reduction were seen more in the VLCD group: 9.7% reduction in total fat mass compared to a 2.0% reduction for the LFD; P-value < 0.001.  HDL-C increased with the VLCD group significantly and decreased results in HOMA-IR, fasting insulin, and triglycerides as compared to LFD. Insulin sensitivity measurement in the VLCD group increased, with a decrease in total cholesterol and LDL-C. As for fasting glucose, no significant changes.   

The authors of the study concluded that patients in the VLCD arm had a significant decrease in weight, along with a 3-fold greater reduction in VAT and IMAT. While VLCD patients showed a decrease in DXA lean mass, a direct measure of thigh skeletal muscle volume via MRI showed no change over 8 weeks, and following adjustment for change in total fat mass, the VLCD group had relatively greater skeletal muscle than the LFD group, which suggests that there was preservation of skeletal muscle during weight loss. Overall, the study provides future insight into obesity in older adults, suggesting that weight loss, body composition, decrease in fat tissue, and improvements in cholesterol and glucose metabolism can help reduce the high risk of cardiometabolic disease. This study’s limitations were not blinded, diets not isocaloric, the food list not provided, and adherence assessed by self-reporting. Future studies must include blindness for all participants and larger sample size. This study is critical because obesity is a worldwide disorder and, if not controlled, can cause patient health to deteriorate.   

Practice Pearls 

• Diets for weight loss will enhance the ability to fight obesity. 
• Low carbohydrate diets reduce weight and body fat, and lower cholesterol in patients with obesity. 
• Insulin sensitivity can be controlled by low carbohydrate diets to regulate blood glucose.  

Goss, A.M., Gower, B., Soleymani, T. et al. Effects of weight loss during a very low carbohydrate diet on specific adipose tissue depots and insulin sensitivity in older adults with obesity: a randomized clinical trial. Nutr Metab (Lond) 17, 64 (2020). https://doi.org/10.1186/s12986-020-00481-9 

Tarshay Boyd PharmD. Candidate, LECOM School of Pharmacy