A controlled study of sleep-deprived young adults has provided the first causal evidence linking the lack of sleep to abdominal obesity and harmful visceral, or ‘belly’ fat. In what the researchers claim is the first-ever study evaluating the relationship between sleep restriction and body fat distribution, they’ve reported the novel finding that the expansion of abdominal adipose tissue, and especially visceral fat, occurred as a function of shortened sleep.
Naima Covassin, PhD, a researcher in cardiovascular medicine at Mayo Clinic in Rochester, Minnesota, led the randomised, controlled study of 12 healthy, nonobese people randomised to controlled sleep restriction — two weeks of four hours of sleep a night — or controlled sleep of nine hours a night, followed by a three-day recovery period. The study was conducted in the hospital setting, monitored participants’ caloric intake, and used accelerometery to monitor energy expense. Participants ranged in age from 19 to 39 years.
“What we found was that at the end of two weeks these people put on just about a pound (0.5 kg) of extra weight, which was significant, [if] very modest,” said senior author Virend K. Somers, MD, PhD, Alice Sheets Marriott Professor in Cardiovascular Medicine at Mayo Clinic.
“The average person who sleeps four hours a night thinks they’re doing OK if they only put on a pound. The problem is that when you do a more specific analysis you find that actually with the one pound the significant increase of the fat is in the belly area, particularly inside the belly,” he said
The study found that the patients on curtailed sleep ate on average an additional 308 calories a day more than their controlled sleep counterparts (95% confidence interval, 59.2 – 556.8 kcal/day; P = .015), and while that translated into a 0.5-kg weight gain (95% CI, 0.1 – 0.8 kg; P = .008), it also led to a 7.8-cm2 increase in visceral adipose tissue (VAT) (95% CI, 0.3 – 15.3 cm2; P = .042), representing an increase of around 11%. The study used CT on day 1 and day 18 (one day after the three-day recovery period) to evaluate the distribution of abdominal fat.
VAT findings post-recovery
After the recovery period, however, the study found that VAT in the sleep-curtailed patients kept rising, yet body weight and subcutaneous fat dropped, and the increase in total abdominal fat flattened.
“They slept a lot, they ate fewer calories and their weight came down, but, very importantly, their belly fat went up even further,” Somers said. On average, it increased another 3.125 cm2 by day 21, a further 50%.
The findings raised a number of questions that need further exploration, Somers said.
“There’s some biochemical message in the body that’s continuing to send fat to the visceral compartment. What we don’t know is whether repetitive episodes of inadequate sleep actually accumulate over the years to give people a preponderance of belly fat,” he said.
The study also showed that the traditional parameters used for evaluating cardiovascular risk are not enough, Somers said.
“If we just did body weight, body mass index, and overall body fat percentage, we’d completely miss this,” he said.
Future investigations should focus on two points, identifying the mechanisms that cause VAT accumulation with less sleep, and whether extending sleep can reverse the process.
“The big worry is obviously the heart. Remember, these are not sick people. These are young healthy people who are doing the wrong thing with their body fat; they’re sending the fat to the completely wrong place,” said Somers.
You can read the full article here: https://www.sciencedirect.com/science/article/abs/pii/S0735109722003102