Time restricted eating over year-long study helped subjects cut fat, but they lost muscle, too

By Hank Schultz

- Last updated on GMT

©Getty Images - Mel Curtis
©Getty Images - Mel Curtis

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A long term study has shown that a time-restricted eating protocol helped strength-training participants lose weight and quell inflammation. But they lost muscle as well as fat, primarily because their testosterone levels were depressed.

The new study was published in the journal Medicine & Science in Sports & Exercise​.  It was the work of researchers associated with institutions in Italy and Texas.

Participants volunteered to extend short term study

The study was an extension of a previous study​ that looked at the effects of time-restricted eating (TRE) on participants who did regular resistance training.  After the conclusion of the initial 8-week study the researchers asked for volunteers to continue the protocol for an additional 10 months. The researchers ended up with two groups of 10 participants, and in the end collected data from 19 subjects.

The subjects were young males (average age, 28) who had been lifting weights for at least 5 years prior to the study, which began in 2014.  The subjects weighed an average of 185 lbs going in and had average body fat percentages of about 14%.

The subjects consumed about 2,900 calories of food a day, with 53% as carbohydrates, 25% as fat and 22% as protein. The normal diet (ND) group took its meals at 8 am, 1pm and 8 pm, whereas the TRE group packed food intake into an 8 hour period, with meals at 1 pm, 4pm and 8 pm.  That group fasted for the remaining 16 hours.

The TRE group at 40% of its calories at ‘breakfast,’ 25% at the second meal and 35% for dinner. The breakdown for the ND group was 25%, 40% and 35%.

The participants continued their accustomed weight training schedules.  Those protocols were set during the initial 8-week study and were continued unsupervised during the 10-month follow up period, with the researchers relying on the high experience of the participants.  All training sessions were conducted between 4pm and 6pm to fall within the feeding window of both groups.

The participants were assessed at baseline, again at 2 months and then had a final visit with the researchers at the end of the 12-month study.  The participants maintained food diaries to judge compliance with the feeding protocol.

In addition to taking biometric readings, the researchers also performed blood analyses. They measured Insulin-like growth factor 1 (IGF-1), testosterone, leptin, adiponectin and blood glucose.  They also assessed total cholesterol, HDL cholesterol, LDL cholesterol, and TG concentration.

The researchers found that the long term TRE group naturally started to eat less that did the ND group.  Over the course of the year they ate on average about 6.4% fewer calories.  This led to a ‘natural’ weight loss of about 3.6% in the TRE group compared to baseline and cut their fat mass by more than 11%.   The ND group, on the other hand, gained weight during the year, adding a bit less than 3% body mass.

The TRE group showed improvements in cholesterol and insulin resistance, and a decrease of inflammatory markers.

But the TRE group also showed a significant drop in free testosterone levels, which dipped by almost 17% during the course of the trial. There was no change in testosterone in the ND group. The TRE group lost muscle mass during the course of the study, though, interestingly those subjects did not lose strength.

No silver bullet

Antonio Paoli, MD, who led the study, said the takeaway is that while TRE can provide some benefits, beware of some of the promises you might find on social media for the approach.

“These findings demonstrated that well-trained resistance exercisers who adhere to a fasting protocol for a long period of time can obtain beneficial effects on health biomarkers and inflammatory indices. Moreover, the long-term time-restricted eating approach spontaneously reduced the total caloric intake, driving a ‘healthy weight loss.’ However, long-term, time-restricted eating negatively affected muscle mass due to the significant negative impact reported on anabolic hormones in this population,” ​he said.

“Our study provides new insight into the management of meal frequency and meal timing for people expert in resistance training activities. The main take-home message is that there are pros and cons to prolonged time-restricted eating. Although time-restricted eating may produce some physiological advantages, it is not a miracle as often suggested in social media posts,” ​Dr Paoli concluded.

Source: Medicine & Science in Sports & Exercise

December 2021 - Volume 53 - Issue 12 - p 2577-2585
Twelve Months of Time-restricted Eating and Resistance Training Improves Inflammatory Markers and Cardiometabolic Risk Factors
Authors: Moro T, et al.

Sports & Active Nutrition Summit USA

Time restricted eating, ketogenic diets and other feeding strategies will be among the topics covered in NutraIngredients-USA's Sports & Active Nutrition Summit USA, which returns in 2022 as an in-person event.  The venue is the Hyatt Regency Hotel on San Diego's beautiful Mission Bay.  The event, which is being produced in cooperation with the American Herbal Products Association's Sports Nutrition Committee, will take place on Feb. 14, 15 and 16.  To sign up for an EARLY BIRD DISCOUNT visit the event homepage​. 

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