America is pretty obsessed with body image.
So most people who go on diets are looking to fit the acceptable mold.
In contrast, medical advice to avoid or shed excess pounds centers on health concerns.
Regardless of the motivation, we're more likely to stick to resolutions with tangible benefits.
And a new study suggests that calorie-cutting leads to better sleep, quality of life, mood, and sex.
One change, multiple benefits
Previous research indicates that calorie restriction can improve quality of life, sleep, and sexual function.
But that research involved overweight and obese participants, so it wasn't clear whether the results apply to people closer to healthy weight.
A study published last year was designed to test the effects of substantial calorie restriction in non-obese people.
Researchers at three universities collaborated on this two-year clinical trial, which involved 218 men and women (Ravussin E. et al. 2015).
Three in four of the participants (70%) were women, and their average age 38.
The participants were either of normal, healthy weight or slightly overweight: their body mass index or BMI ranged from 22 to 28.
Two thirds of participants were assigned to cut their calorie intake by 25% over the course of two years.
Meanwhile, the remaining third — the control group — maintained their normal diet for two years.
At the start of the study, after one year, and at the end of the two-year study, all participants were given questionnaires designed to gauge mood, sleep, sexual function, and overall quality of life.
Likewise, body-weight data was collected at the study's outset, and after one year and two years.
After two years, the calorie-restriction group lost an average of 16.7 pounds compared with less than a pound in the control group.
And, compared with the control group, the calorie-restriction group reported improved sleep at year one, and higher energy levels, better mood, stronger sex drive, less tension, and improved general health after two years.
It has been thought that calorie restriction in adults of normal weight might yield negative outcomes, including poor sleep, low energy, and decreased sexual drive.
In fact, the opposite was true.
But the researchers detected no downside:
"… the results of the present study indicate that two years of CR [calorie restriction] is unlikely to negatively affect these factors in healthy adults; rather, CR is likely to provide some improvement.”
Long-term benefits of calorie restriction
Much of the evidence on calorie restriction has come from animal research.
However, a 2015 study from the National Institutes of Health found that calorie restriction may lower the risk factors for certain age-related illnesses in people.
The results showed that calorie restriction in normal-weight and moderately overweight people lowered key risk factors for age-related diseases and premature death, including cholesterol levels, blood pressure, and insulin resistance.
This human trial also tested the effects of calorie restriction on resting metabolic rate (after adjusting for weight loss) and body temperature, which are reduced in many animal studies, and these effects may contribute to enhanced longevity.
While the NIH researchers expected to find an impact on human metabolism with calorie restriction, the results were not conclusive.
However, calorie restriction did lower several risk factors for cardiovascular disease compared to the control group:
- Blood pressure fell by 4%
- Total cholesterol fell by 6%
- Levels of C-reactive protein — a marker of inflammation linked to heart disease — dropped by 47%.
In addition, calorie restriction significantly lowered insulin resistance, which is a key indicator of diabetes risk.
- Martin CK, Bhapkar M, Pittas AG, et al. Effect of Calorie Restriction on Mood, Quality of Life, Sleep, and Sexual Function in Healthy Nonobese Adults: The CALERIE 2 Randomized Clinical Trial. JAMA Intern Med. Published online May 02, 2016. doi:10.1001/jamainternmed.2016.1189.
- Ravussin, E., et al. A 2-Year Randomized Controlled Trial of Human Caloric Restriction: Feasibility and Effects on Predictors of Health Span and Longevity. J Gerontol A Biol Sci Med Sci (2015) 70 (9): 1097-1104. doi: 10.1093/gerona/glv057