Welcome to the February 2021 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.

Because February is American Heart Month, this issue focuses on new studies that look at various aspects of cardiometabolic health: (1) omega-3 levels and heart rate recovery, (2) brown fat and type 2 diabetes risk, (3) high-intensity exercise and metabolism, and (4) weight loss and fatty liver.

Higher omega-3 levels benefit heart rate recovery in healthy adults

Omega-3 fatty acids have many health benefits, including for cardiovascular health.* A new study adds to our knowledge in this area by showing the relationship between omega-3 index (O3I) and heart rate recovery from exercise.

Heart rate recovery (HRR) is a measure of the how well the heart returns to its resting state after exercise. It is also thought to be reflective of the balance between sympathetic and parasympathetic activity in the nervous system. Poor HRR is correlated with an increased risk of cardiovascular events and all-cause mortality.1 Thus, measuring and improving HRR should be a health goal for many adults seeking to live a longer and healthier life.

The O3I is a measurement of the cumulative percentages of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in the membranes of red blood cells. The percentage is inversely correlated with cardiovascular events; i.e., higher percentages are strongly correlated with lower a risk for overall cardiovascular disease.2 The average 03I in the United States is about 4.5 percent, while a desirable level for maintaining good cardiovascular health is believed to be above 8 percent.

In the new study,3 published in November 2020, researchers at the Cooper Institute in Texas evaluated data from 14,000 healthy adults (one-third women, two-thirds men; mean age 50) who were subjected to a maximal exercise test. Overall, a higher O3I was associated with better HRR in both sexes. Better HRR was also associated with healthier BMI, blood pressure, and blood fats (triglycerides, LDL-, and HDL-cholesterol). The researchers concluded that a higher O3I is likely a good measure of cardio-protection in generally healthy adults. A 2018 study found that a dose of two grams of fish oil daily resulted in a 3-percent increase in O3I over 13 weeks.4

Note: William Harris, one of the authors of the November 2020 study, is credited with developing the O3I, which is a potential conflict of interest for this data.

Contributed by Jacqueline Jacques, ND


  1. Qiu S, Cai X, Sun Z, et al. Heart rate recovery and risk of cardiovascular events and all‐cause mortality: a meta‐analysis of prospective cohort studies. J Am Heart Assoc 6(5):e005505. doi:10.1161/JAHA.117.005505
  2. The omega-3 index: a novel way to determine cardiovascular risk Cooper Institute. https://www.cooperinstitute.org/2016/10/14/the-omega-3-index-a-novel-way-to-determine-cardiovascular-risk [Accessed January 25, 2021]
  3. Farrell S, DeFina L, Tintle N, et al. Higher omega-3 index is associated with more rapid heart rate recovery in healthy men and women. Prostaglandins Leukot Essent Fatty Acids 2020;163. doi:10.1016/j.plefa.2020.102206
  4. Walker R, Jackson K, Tintle N, et al. Predicting the effects of supplemental EPA and DHA on the omega-3 index. Am J Clin Nutr 2019;110(4):1034-1040.

Brown fat improves cardiometabolic health

Several recent studies have stimulated interest in the potential health benefits of brown fat, one of several types of fat (adipose), including white adipose, brown adipose, and beige adipose. White adipose is stored as fat and calories in the body, while brown and beige adipose are thermogenic – releasing the fat from storage and dissipating it as heat.

A recent study sought to determine if the presence of brown adipose tissue (BAT) is protective against cardiometabolic diseases. Body scans of 52,487 patients were analyzed retrospectively for BAT (scans had previously been conducted to diagnose or follow cancer treatments at Memorial Sloan Kettering Cancer Center). Presence or lack of BAT was then correlated with disease risk.

The researchers found that brown and beige fat decreased the overall prevalence of cardiometabolic disease and conferred decreased odds of developing conditions like type 2 diabetes, hyperlipidemia (high cholesterol and/or triglycerides), coronary artery disease, cerebrovascular disease, and hypertension. For example, 4.8 percent of the patients with high brown fat developed type 2 diabetes, compared to 9.5 percent of those without significant brown fat. These results were more pronounced in obese individuals; for example, individuals who were obese but had brown fat had only slightly increased risk for developing type 2 diabetes when compared to normal weight individuals who had no brown fat.

This raises the question of what stimulates a person to create brown fat. The best-known stimulator of brown fat is cold exposure, which was highlighted in recent research summarized in the December 2020 issue of Research Extracts here at Take 5 Daily. Exercise stimulates brown fat production in rodents, and is believed to do the same in humans, but this research is still in its infancy, as is research to discover other means to stimulate brown fat.

Contributed by Kathi Head, ND


  • Becher T, Palanisamy S, Kramer D, et al. Brown adipose tissue is associated with cardiometabolic health. Nat Med 2021;27(1):58-65. 

Does high intensity exercise regulate post-meal metabolism better at colder temperatures?

Metabolism of carbohydrates and lipids, particularly the increase of fats in the bloodstream after eating, is a potential indicator for the development of type 2 diabetes, liver disease, and cardiovascular disease. High intensity exercise and cold temperature exposure have been shown to have positive effects on the metabolism of fats and carbohydrates, both during exercise and after meals. A recent study sought to determine whether high intensity exercise in a cold temperature environment could create a greater impact on fat metabolism after a meal than high intensity exercise alone.

Participants in the study included males and females, ages 18-30, who were moderately fit but not formally trained athletes. High intensity interval exercise sessions were conducted in both cold temperature and neutral temperature settings, each one week apart. Metabolic and energy expenditure testing was conducted at rest, during exercise, and after exercise. In addition, on the morning following each exercise session, participants were fed a high-fat meal. Blood samples were obtained during each exercise session and before and after the high-fat meal.

Study results showed that high intensity exercise in cold temperatures improved lipid metabolism by 358 percent during the exercise session. However, for post-meal metabolism, improvements with cold temperature exercise were not significantly better than neutral temperature. The authors noted several reasons why post-meal metabolism might have been similar for both temperature conditions – the body’s use of muscle lipids as a fuel source during high intensity exercise, consumption of a post-exercise meal bar leading to a smaller energy deficit, and a relatively short amount of cold temperature exposure.

Contributed by Jennifer L. Greer, ND, MEd


  • Click here for full text.
  • Munten S, Ménard L, Gagnon J, et al. High-intensity interval exercise in the cold regulates acute and postprandial metabolism. J Appl Physiol (1985). 2020;10.1152/japplphysiol.00384.2020. doi:10.1152/japplphysiol.00384.2020

Meta-analysis suggests weight loss is beneficial in fatty liver 

A recent meta-analysis evaluated evidence from 43 international studies, including 2,809 participants, that investigated the relationship between weight loss and non-alcoholic fatty liver disease (NAFLD).

The participants had an average baseline BMI of 32.8 (± 8.3), average age of 46.8 (± 11.6) years, and 44 percent were female; 24 percent of participants had diabetes and 35 percent had hypertension. Studies involved a variety of weight loss strategies, including behavioral, pharmacological, and bariatric surgery.  Median follow-up was six months, with bariatric study follow-up generally longer than the other strategies. Significant weight loss was achieved in all interventions, with surgical tending toward greater reductions.

The study found significant reductions in disease markers were associated with modest weight loss. The first five kg (11 pounds) of weight loss yielded an average improvement in steatosis (accumulation of excess fat in the liver) of five percent, with each six kg (3.2 pounds) afterward associated with an additional five-percent reduction – a significant rate of 0.77 percent per one kg (2.2 pounds) of weight loss. Alanine transaminase (ALT), a marker of liver injury or disease, was reduced an average of 12 units/liter (U/L) with the first four kg (8.8 pounds) of weight loss, with an average of 0.83 U/L per one kg (2.2 pounds) overall. Similarly, aspartate transaminase (AST) was lowered by an average of 7 U/L for the first two kg (4.4 pounds) of weight loss, with an overall average of 0.56 U/L per one kg (2.2 pounds). A dose-response effect between weight loss and several additional markers of disease, including inflammation, ballooning (enlarged liver cells), and resolution of NAFLD/NASH (non-alcoholic steatohepatitis), was also observed. The type of weight loss intervention did not make a significant difference in result.  The effects appeared to have been slightly greater in participants of Asian descent.  

Contributed by Sheena Smith, MS MA 


  • Koutoukidis D, Koshiaris C, Henry J, et al. The effect of the magnitude of weight loss on non-alcoholic fatty liver disease: A systematic review and meta-analysis. Metabolism 2021;115:154455. doi:10.1016/j.metabol.2020.154455

Looking to improve metabolic parameters associated with good health? Consider the Thorne Weight Management Bundle. Do you need more guidance in terms of diet and lifestyle approaches to healthy weight? Check out our Wellness Guides, including Weight Management and Metabolic Syndrome guides.

Are you unsure where to start? Find out how your weight-related biomarkers stack up with this at-home test that provides you analysis of results along with diet, lifestyle, and supplement recommendations.