Welcome to the December 2020 edition of Research Extracts. “The Extracts” is designed to keep busy practitioners and savvy consumers up to date on the latest research on diet, nutrients, botanicals, the microbiome, the environment, and lifestyle approaches to good health. Our medical team, which includes NDs, MDs, PhDs, RDs, an MS, and an LAc, has summarized the essence of several of the most interesting studies.

Probably more appropriate for after the holiday season, rather than now with the season’s edible goodies surrounding us, the first three studies discuss various aspects of fat metabolism and weight, including studies on (1) cold exposure, vitamin A, and fat, (2) which gut bacteria might prevent obesity, and (3) does intermittent fasting work to lose weight. Fourth in line is a study on the potential cellular anti-aging effects of hyperbaric oxygen.

The effect of cold exposure on fat burning and what vitamin A has to do with it

There are two types of fat – white adipose and brown adipose. White adipose is stored as fat and calories in the body, but when energy/heat production (thermogenesis or fat burning) takes place the white adipose turns to brown fat. But what stimulates it to turn brown or activates already existing brown fat? This study, conducted at the Medical University of Vienna, with contributors from Harvard Medical School, Rutgers University, and Brigham and Women’s Hospital, looked at the effects of cold exposure on thermogenesis in mice and humans.

In the human arm of the study, 30 healthy, lean volunteers (ages 20-45) were exposed to moderate cold (57-62 degrees F) for 2.5 hours from water-perfused cooling vests. These temperatures have been shown in previous studies to stimulate brown fat production, which in turn has been shown to stimulate fat loss. 

Vitamin A (retinol) metabolism is known to play a role in adipose tissue activation. In this study, cold exposure led to significantly increased blood levels of retinol and retinol binding protein (RBP). RBP is necessary for transporting vitamin A from the liver (where it’s stored), to other tissues in the body, including adipose tissue. Furthermore, the researchers reported that, “Retinol promotes browning in human adipocytes with coordinated increases in oxidative metabolism,” which was measured in adipocyte precursor cells from four donors. The mice studies confirmed these findings.

What this study does not say is take vitamin A and you’ll burn more fat. In the United States, vitamin A deficiency is uncommon. Eating a balanced diet plus taking a good multi-vitamin should be sufficient for most adults. What this study does say is that exposure to cold – perhaps best achieved in winter by exercising outdoors – can stimulate vitamin A release from the liver, thus promoting fat metabolism. 

The researchers conclude: “Systemic vitamin A levels are regulated by cold exposure in mice and humans, and intact retinoid transport is essential for cold-induced adipose tissue browning and adaptive thermogenesis.”

Contributed by Kathi Head, ND


The protective effect of the gut bacteria Akkermansia against obesity declines with age

Certain species of gut bacteria are associated with obesity. One such species, Akkermansia, is recognized as being protective against the development of obesity, and levels of Akkermansia in the intestinal microbiome are inversely associated with metabolic syndrome. Obesity, however, has a variety of contributing environmental factors, some of which alter gut microbiome composition.

A recent cross-sectional analysis used information from the American Gut Project (a database with over 10,000 participants) to determine how obesity risk is altered by presence of the Akkermansia species and environmental factors like age, smoking status, diet, location, and alcohol use. Several findings were reported:

  1. Higher levels of Akkermansia were more likely to be found in individuals who were younger, female, nonsmokers, or those who didn’t follow a vegetarian diet
  2. BMI and Akkermansia levels were inversely correlated (p<0.001), indicating a protective effect of the species against obesity
  3. The protective effect of Akkermansia against obesity was not changed by the environmental factors of smoking frequency, alcohol use, diet type, and country of residence
  4. A 10-percent increase in Akkermansia was associated with a 26-percent average reduction in obesity risk
  5. Aging weakened, but did not remove, the protective effects of Akkermansia against obesity

 Contributed by Jennifer Greer, ND, MEd


  • Link here for full text
  • Zhou Q, Zhang Y, Wang X, et al. Gut bacteria Akkermansia is associated with reduced risk of obesity: evidence from the American Gut Project. Nutr Metab (Lond) 2020;17:90. doi:10.1186/s12986-020-00516-1

Can time-restricted eating help with obesity and metabolic health?

Time-restricted eating (or intermittent fasting) is a recent dietary trend that has many adherents in the world of nutrition. The general principle is to intersperse defined periods of fasting (typically in the range of 12-48 hours) while eating a diet that is or is not restricted in other ways. Some animal data indicates this to be a useful strategy for weight loss.1   

A recent human study analyzed if intermittent fasting benefits overweight or obese adults.2 Researchers followed 116 men and women divided into two groups: one group ate three meals daily at consistent times, while the other group followed a time-restricted eating pattern where they ate ad libitum from noon until 8 pm, then fasted from 8 pm until noon the following day. Subjects were followed for 12 weeks and tracked for weight, fat mass, lean mass, fasting insulin, fasting glucose, hemoglobin A1c levels, estimated energy intake, total energy expenditure, and resting energy expenditure.

Although overall there was slightly more weight loss in the time-restricted eating group, the difference in weight loss between the two groups was not significant. In addition, there was no change in fat mass in either group; although there was a greater loss of lean mass in muscles of the upper and lower limbs in the intermittent fasting group that was significant compared to the control.

This is the second human study3 that shows a loss of lean mass with intermittent fasting – a rather disconcerting trend. Finally, no significant changes were demonstrated in metabolic health measurements or in sleep, although there was a measured reduction in physical activity (measured via Oura ring data) that led to lower total energy expenditure.

Overall, this study does not support a benefit of time-restricted eating as a treatment for obesity, and, like a prior study, raises the question about a possible risk for reduced lean mass.   

Contributed by Jacqueline Jacques, ND


  1. Chaix A, Zarrinpar A, Miu P, Panda S. Time-restricted feeding is a preventative and therapeutic intervention against diverse nutritional challenges. Cell Metab 2014;20(6):991-1005. 
  2. Lowe D, Wu N, Rohdin-Bibby L, et al. Effects of time-restricted eating on weight loss and other metabolic parameters in women and men with overweight and obesity: The TREAT Randomized Clinical Trial. JAMA Intern Med 2020;180(11):1491-1499. 
  3. Harris L, Hamilton S, Azevedo LB, et al. Intermittent fasting interventions for treatment of overweight and obesity in adults: a systematic review and meta-analysis. JBI Evid Synth 2018;16(2):507-547. 

Hyperbaric oxygen shows positive effects on telomere length and cellular senescence 

Of the many signs of aging, two important events are not visible to the naked eye. One is related to the ends of the chromosomes, called telomeres. Aging causes telomeres to become shorter, reducing their ability to protect the DNA in the chromosome. Aging also results in the inability of cells to replicate (make new copies), called senescence.

When a cell becomes senescent, it is still alive and functional, but it has lost the ability to replicate. Healthy cellular replication is an important aspect of organ and tissue health. Previous studies have shown potential anti-aging benefits from hyperbaric oxygen (100% oxygen at higher than normal pressure), including potential positive impacts on telomeres and senescence.  

A study including 30 individuals (ages 64 and over) investigated whether daily hyperbaric oxygen treatment had any impact on telomere length (longer is better) or accumulation of senescent cells (fewer is better). Each participant received a hyperbaric treatment five days per week over three months for a total of 60 sessions. White blood cells (specifically T-helper cells, T-killer cells, B cells, and natural killer cells) were collected and analyzed at baseline, after 30 and 60 treatments, and 1 to 2 weeks following the last treatment.  

Data from 25 individuals was available for analysis of telomere length. Significant increases in telomere length compared to baseline were seen for all four immune cell types, with the greatest effect observed in B cells. Data from 20 individuals was available for analysis of senescence. Only the two T-cell types were evaluated, with a significant decrease in the number of senescent cells (as a percent of total) found in both cell types for the post-treatment time point compared to baseline.

The T-killer cell subpopulation showed significantly reduced senescent cells throughout the study. The authors acknowledged that small sample size and lack of control group were important limitations of this study; however, they suggest that hyperbaric oxygen treatment warrants further study as a viable strategy to offset some effects of aging.  

Contributed by Sheena Smith, MS MA


  • Click here for full text
  • Hyperbaric oxygen therapy increases telomere length and decreases immunosenescence in isolated blood cells: a prospective trial. Aging (Albany NY). 2020 Nov 18;12. doi: 10.18632/aging.202188.