Newsletter #151: Understanding BMI & Health 🤔
Happy weekend friends, and welcome once again to the newest edition of the humanOS newsletter. Hope this email finds you well!
This week, we looked at some recent studies examining the consequences of elevated body mass index (BMI). This is a little more complicated than you might think, due to the complex interactions of BMI with age, smoking, and other risk factors.

You may have heard that some epidemiological studies have suggested that there is an “obesity paradox,” wherein people with a higher body mass are actually at reduced risk of mortality, compared to those at a “normal” body mass. Does this mean that it’s actually better to be “overweight?” Are our ideas of an ideal BMI off base?
In order to answer this question, we probably need to take a closer look at the context. It has been known for some time that weight loss later in life is often unintentional, and frequently associated with a multitude of severe chronic diseases which may not even have been diagnosed yet. In other words, an association of low BMI with higher mortality in such individuals may actually be due to illness, rather than their weight per se. On the other hand, randomized controlled trials show that intentional weight loss, due to healthy lifestyle interventions, reduces risk of cardiovascular disease markers and mortality. It also makes sense to look at the long-term life-course of BMI within individuals from childhood to old age. That way, we can examine the effect of weight and weight loss early in life, which is more likely to capture changes in fat mass rather than the hidden toll of disease, and we can also see how body mass affects health over the course of decades.
To learn more about what research shows on this, scroll down👇🏼
This Week’s Research Highlights
🫀 Maintaining a stable BMI in the normal range over one’s life is associated with the lowest cardiovascular risk.
Researchers examined longitudinal data from the China Health and Nutrition Survey (n = 5276), which collected up to seven measurements of BMI between 1989-2009. Cardiovascular risk factors, including high blood pressure, high blood glucose, and high blood lipids, were assessed in 2411 of the participants at the end of the study period. The researchers analyzed how these BMI measurements changed over the passage of time, and identified four characteristic BMI trajectory patterns - meaning distinct subgroups of individuals following a similar pattern of BMI across the life course (age 6-80). These patterns included: Normal-Stable (22.4% of the total participants), Low normal-Normal-Stable (44.1%), Low normal-Normal-Overweight (27.2%), and Overweight-Obese (4.3%). They then analyzed how these trajectory patterns were associated with aforementioned cardiovascular risk markers. Being in the Normal-Stable group - meaning having a stable BMI that remained within the normal range over the course of one’s life - was found to be associated with the lowest cardiovascular risk, while being in the Overweight-Obese pattern (being overweight early in life but gradually becoming obese with age) was associated with the greatest risk of high blood pressure, high blood glucose, abnormal blood lipids, and multiple cardiovascular risk factors.
𐄷 More years spent at an obese BMI is linked to worse values for multiple cardiovascular risk factors.
Researchers analyzed body mass index (BMI) and cardiometabolic disease risk factor data enrolled in three British birth cohort studies (n = 20746). Within each cohort, individual life course BMI trajectories were created between 10 and 40 years of age. From these, the researchers captured age of obesity onset and duration of time spent obese, and they examined how obesity duration correlated with blood pressure, HDL-C, and glycated hemoglobin (HbA1c). Sure enough, they found that greater obesity duration was associated with worse values for all of the cardiometabolic risk markers that they looked at. The strongest association with obesity duration was for HbA1c: HbA1c levels in those with obesity for <5 years were 5% higher (compared with those who were never obese), but were 20% higher in those with obesity for 20 to 30 years. This finding lines up with the study described above, which found that those whose BMI remained overweight or obese over the entire life course were at the greatest cardiovascular risk. This is also concerning because the obesity epidemic is increasingly affecting younger individuals - meaning that more and more people may accumulate decades of exposure to obesity in their lifetimes.
🩺 Treating obesity early in life results in a dramatic reduction in mortality risk.
Researchers analyzed data from a nationally representative cohort of participants in the National Health and Nutrition Examination Survey (NHANES), who were followed for a mean of 10.7 years (n = 24205). Weight history in these individuals was assessed by self-reported weight at age 25, at baseline, and ten years before baseline. The researchers examined the relationship between changes in BMI and the likelihood of a participant dying over the observed period. After controlling for other potential confounding variables (such as sex, smoking, education), they found that participants whose BMI was reduced from the “obese” range at age 25 down to the “overweight” range at midlife were 54% less likely to have died, compared to those whose BMIs remained at the “obese” range. Furthermore, these subjects achieved a similar level of risk to those who maintained a BMI at the overweight range.
🩸 Exercise is good for everyone - but it doesn't fully reverse the negative effect of excess weight.
Researchers looked at data from working adults insured by a large occupational risk prevention company in Spain (n = 527662). These subjects underwent annual medical examinations as part of their health insurance coverage, offering data on their BMI as well as cardiovascular risk factors, and they were also asked about their physical activity levels. Participants were grouped by BMI, activity levels, and cardiovascular health. After adjusting for other variables (age, sex, smoking status), the researchers found that for all BMI categories, any level of physical activity was linked to lower odds of diabetes, high cholesterol, or high blood pressure. Benefits also accrued in a dose-dependent manner - more physical activity was better than less. However, participants in the overweight and obese categories were at greater cardiovascular risk than counterparts with a normal BMI, regardless of physical activity. For instance, compared to individuals who were at a normal weight and were inactive, subjects with obesity who were physically active still had two-fold higher risk of high cholesterol, five-fold higher risk of hypertension, and four-fold higher risk of type 2 diabetes.
Question of the Week
🤔 When we lose weight (more precisely, when we burn body fat), where exactly does it go?
💡 Answer
Podcasts We Loved This Week
- Herman Pontzer: Metabolism, mitochondria, and evolutionary biology. Via Sigma Nutrition Radio.
- Saad Omer: The global COVID-19 supply problem. Via Science Friday.
Products We Are Enjoying
Instant Pot Duo Nova Pressure Cooker 7 in 1
This device is remarkably versatile - functioning as a rice cooker, pressure cooker, and steamer all in one. It’s also energy-efficient, super easy to use, and can cook things like legumes, grains, potatoes, tubers, etc. really fast without requiring much effort on your end.
Good for those of us who want to eat healthy without putting in a lot of work.

humanOS Catalog Feature of the Week
The FLASH Diet
This week, we’d like to highlight one of the courses from the Ideal Weight Program, developed by our good friend Stephan Guyenet, a researcher who specializes in the neuroscience of eating behavior and obesity. The Ideal Weight Program is an evidence-based system for sustainable weight management which teaches you the science of body weight regulation and eating behavior and translates it into simple, practical strategies for weight management. This program offers three different diets based on your weight management goal. For those who need to lose body fat relatively rapidly (but safely), the FLASH Diet is the plan for you.
FLASH stands for Fat Loss And Sustainable Health, and is modeled after protein-sparing modified fast diets that were developed by researchers in the 1970s and remain the most effective fat loss plan ever studied. In this course, Stephan explains the background behind FLASH diet, where it fits in the sequence of the Ideal Weight Program, what to eat and how to prepare food to adhere to this plan, and more.