Study: BMI Is a Good Measure of Health After All


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A simple measure based on weight and height, BMI is widely used to assess if a person is of a healthy weight. But its reliability as a health measure is often criticised, as it does not distinguish fat from muscle and does not tell us where body fat is stored.

Using body scans from 2,840 young people aged 10 and 18 in Bristol’s Children of the 90s population study, researchers examined BMI findings against more detailed measures of fat.

They studied the effects of total fat, along with fat in the trunk, arms and legs, on 230 different traits relevant to metabolism and future heart disease risk, such as cholesterol and blood pressure. These effects were compared with those seen when using BMI as a measure.

The study, published in the Journal of the American College of Cardiology, found that higher total fat at age 10 and 18 was associated with damaging levels of cardiometabolic traits such as higher blood pressure and adverse cholesterol and inflammatory profiles at age 18.

Effects appeared to worsen with time and were driven most by fat stored and gained in the trunk, although gains in leg fat also appeared harmful. Carrying more lean mass (assessed here as anything in the body that that isn’t fat or bone) had less of an impact on traits and did not appear to protect against carrying more fat. Higher BMI showed similar effects as higher total and trunk fat, reflecting close overlap between these measures.

Dr Joshua Bell, an epidemiologist at the University of Bristol who led the study, commented: “BMI is often criticized. Our study asked how useful it really is for detecting the health effects of obesity by pitching it against more objective body scan measures. We found that trunk fat is the most damaging to health, but that simple BMI gives very similar answers to more detailed measures. This is good news since BMI is widely measured and costs virtually nothing.”

“We’re now in a better position to understand obesity in the young thanks to participants of the Bristol-based Children of the 90s study – they, and all study participants, make new insights possible.”

“We now need to look at more detailed lean measures to see if other aspects protect against higher fat, and how this might differ between the sexes. This is more important than ever given stubbornly high rates of obesity worldwide.”

Source: University of Bristol

The Metabolome: A Way to Measure Obesity and Health Beyond BMI

The link between obesity and health problems may seem apparent. People who are obese are at higher risk of type 2 diabetes, liver disease, cancer, and heart disease. But increasingly, researchers are learning that the connection is not always clear-cut. For this reason, they’ve sought to develop better ways to determine who is at an elevated risk of developing these complications.

The current standard for determining obesity is body mass index (BMI), a simple mathematical formula that uses weight and height. Now a paper appearing October 11 in the journal Cell Metabolism is reporting a large study of new ways to measure obesity. The study looked at both the metabolome and the genome, and their relationship to BMI.

“We are attempting to identify the heterogeneity in what we currently call obesity. There’s a need for more precise ways of measuring,” says senior author Amalio Telenti (@atelentia), a genomics professor at Scripps Research. “Although it’s clear that obesity is linked to certain diseases, not everybody who is obese will have these consequences. Also surprising, you may not look obese but still have the problems of someone who is.”

The metabolome is the sum of all the small-molecule chemicals found in a biological sample, often the blood plasma. These chemicals include fatty acids, amino acids, sugars, and vitamins, to name a few. The metabolome changes in response to interactions between the genome and the environment. Those who study metabolomics say it’s poised to become an important part of personalized medicine, along with genomics, proteomics, and analysis of the microbiome.

In the current study, the investigators used data from TwinsUK, a multiyear study examining the genetic and environmental influences on human health and aging. They analyzed body and metabolic measures from nearly 2,000 adult twins that had been collected at three time points over an average of 13 years. They also used data from a single time point for 427 volunteers. They found that about one-third of the metabolites included in the study were associated with changes in BMI.

“For most people, we found the metabolome is tied very closely to weight and BMI,” Telenti explains. “Every time someone gains or loses a pound, their metabolome changes. It’s almost linear.” But at the same time, he adds, “correlating well is not the same as correlating perfectly, and that’s where this work became very interesting.”

“There have been studies before of individuals whose BMI doesn’t match their metabolic health, but this is a new way of defining who is metabolically healthy,” says first author Liz Cirulli (@ETCirulli), a research scientist at Human Longevity Inc. “All across the weight spectrum, we found people who were heavier or lighter than expected based on their metabolome.” These differences were found in a range of metabolites linked to various diseases.

A surprising finding was that genetics didn’t correlate nearly as closely as expected. Differences in genetics between obese and non-obese populations didn’t show patterns that were distinct enough to be predictive. The exception was with a few particular genes known to be connected with extreme obesity, such as mutations in MC4R. This gene is known to play a critical role in regulating food intake and energy balance.

Telenti stresses that the metabolome tests developed for this paper are still an academic development, and much more research is needed before they can be validated and established for clinical use. But eventually, the hope is that it will be possible for someone to get a comprehensive analysis of all the metabolites in their body with one blood test, rather than the battery of tests that’s currently part of a standard physical exam.

Cirulli says that future work will look at defining metabolic signatures for other traits, including blood pressure and android/gynoid ratios — a measure of different types of body fat. In addition, she explains, “It’s important to collect additional longitudinal data in bigger cohorts to see what the long-term health consequences of different metabolic states are.”

Source: Science Daily


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Meal Frequency and Timing Linked to BMI

A study by researchers from Loma Linda University School of Public Health and the Czech Republic has found that timing and frequency of meals play a role in predicting weight loss or gain.

Using information gleaned from more than 50,000 participants in the Adventist Health Study-2 (AHS-2), the researchers discovered four factors associated with a decrease in body mass index: eating only one or two meals per day; maintaining an overnight fast of up to 18 hours; eating breakfast instead of skipping it; and making breakfast or lunch the largest meal of the day. Making breakfast the largest meal yielded a more significant decrease in BMI than did lunch.

The two factors associated with higher BMI were eating more than three meals per day — snacks were counted as extra meals — and making supper the largest meal of the day.

As a practical weight-management strategy, Hana Kahleova, MD, PhD, recommends eating breakfast and lunch, skipping supper, avoiding snacks, making breakfast the largest meal of the day and fasting overnight for up to 18 hours. A postdoctoral research fellow at LLUSPH when the study was conducted, Kahleova is now director of clinical research for the Physicians Committee for Responsible Medicine in Washington, DC, and is currently on sabbatical from the Institute for Clinical and Experimental Medicine in Prague, Czech Republic, as a postdoctoral research fellow and diabetes consultant physician.

Kahleova says the findings confirm an ancient nutritional maxim: “Eat breakfast like a king, lunch like a prince, and dinner like a pauper.”

Titled “Meal frequency and timing are associated with Body Mass Index in the Adventist Health Study-2,” the study was co-written by Gary Fraser, MBChB, PhD, a professor at LLU Schools of Medicine and Public Health, and director of AHS-2. It was published as an online advance on July 12 and will appear in the Sept. 2017 edition of the Journal of Nutrition.

Fraser said that irrespective of meal pattern, there was, on average, an increase in weight gain year by year until participants reached the age of 60. After age 60, most participants experienced a weight loss each year.

“Before age 60 years, those eating calories earlier in the day had less weight gain,” Fraser said, adding that after age 60, the same behavior tended to produce a larger rate of weight loss than average. “Over decades, the total effect would be very important.”

The team employed a technique called linear regression analysis and adjusted their findings to exclude demographic and lifestyle factors that might skew the results.

Source: Science Daily


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Higher BMI Linked with Increased Risk of High Blood Pressure, Heart Disease, Type 2 Diabetes

Results of a new study add to the evidence of an association between higher body mass index (BMI) and increased risk of cardiometabolic diseases such as hypertension, coronary heart disease, type 2 diabetes, according to a study published by JAMA Cardiology.

A connection between higher BMI and cardiometabolic disease risk usually arise from observational studies that are unable to fully account for confounding by shared risk factors. Mendelian randomization (a method of analysis using genetic information) is an approach that partially overcomes these limitations. Using mendelian randomization, Donald M. Lyall, Ph.D., of the University of Glasgow, Scotland, and colleagues conducted a study that included 119,859 participants in the UK Biobank (with medical, sociodemographic and genetic data) to examine the association between BMI and cardiometabolic diseases and traits.

Of the individuals in the study, 47 percent were men; average age was 57 years. The researchers found that higher BMI was associated with an increased risk of coronary heart disease, hypertension, and type 2 diabetes, as well as increased systolic and diastolic blood pressure. These associations were independent of age, sex, alcohol intake, and smoking history.

The authors write that the results of this study has relevance for public health policies in many countries with increasing obesity levels. “Body mass index represents an important modifiable risk factor for ameliorating the risk of cardiometabolic disease in the general population.”

A limitation of the study was that the sample lacked data on a complete range of potential mediators, such as lipid traits and glucose levels.

Source: The JAMA Network

Study Finds More Accurate Way to Determine Adolescent Obesity

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The body mass index calculations that physicians have been relying on for decades may not be accurate for assessing body fat in adolescents between the ages of 8 and 17.

A new study published today in the Journal of the American Medical Association Pediatrics shows that tri-ponderal mass index estimates body fat more accurately than the traditional BMI in adolescents.

These new findings are timely as diagnosing, treating and tracking the prevalence of children and adolescents with obesity is a high public health priority. Moreover, many school districts are sending home report cards labeling adolescents as overweight — a practice that has been controversial because children and adolescents tend to be more vulnerable to weight bias and fat shaming than adults.

bmi tmi graphic“Treating obesity in adolescents requires an accurate diagnosis first,” said lead scientist Courtney Peterson, Ph.D., an assistant professor in the School of Health Professions at the University of Alabama at Birmingham. “We found that TMI is both more accurate and easier to use than BMI percentiles. These new findings have the power to potentially change the way we diagnose obesity in children and adolescents ages 8 to 17.”

BMI is the standard used worldwide to screen for obesity in both children and adults, despite prior evidence that it does not work as well in adolescents. To test BMI accuracy in adolescents, researchers compared body composition data from 2,285 Caucasian individuals ages 8 to 29 who participated in the 1999-2004 U.S. National Health and Nutrition Examination Survey (NHANES). Their findings challenge the accuracy of BMI (weight in kilograms divided by height in meters squared) in adolescents and show that TMI (weight divided by height cubed) estimates body fat more accurately than BMI in those 8 to 17 years old.

“BMI is a pretty good tool for determining whether adults are overweight or obese,” Peterson said. “But we’ve always kind of known that it doesn’t work as well in children.”

Using three different calculations — stability with age, accuracy in estimating percent body fat and accuracy in classifying adolescents as overweight versus normal weight — researchers compared BMI to several different obesity indices. They found that TMI is the best overall body fat index to use in Caucasian adolescents between the ages of 8 and 17.

The researchers found that TMI better estimates body fat percentage, especially in male adolescents for whom the investigators found BMI to be particularly inaccurate. Their analysis also showed TMI to be a better index for diagnosing overweight adolescents than the current BMI percentiles. Using BMI percentiles, researchers noted that adolescents are incorrectly diagnosed as overweight 19.4 percent of the time, versus an only 8.4 percent incorrect overweight diagnosis rate for TMI. The data showed this is especially true for lean adolescents, a significant fraction of whom are incorrectly being diagnosed as overweight.

The researchers also used mathematical strategies to show how the relationship between body weight and height is much more complex in children and adolescents than it is in adults, particularly when adolescents are rapidly growing. The authors explained that for decades this complexity made it challenging to figure out the optimal body fat index for adolescents.

Steven Heymsfield, M.D., one of the team’s physician scientists at LSU’s Pennington Biomedical Research Center, added that, to make BMI work in children, complicated BMI percentiles called “Z scores” were developed to diagnose overweight status and obesity based on BMI levels specific to a child’s age and gender. But the researchers found that using percentiles does not solve BMI’s accuracy problems.


“These findings are important. Many school districts send home report cards labeling adolescents as overweight, and children and adolescents tend to be more vulnerable to weight bias and fat shaming than adults.”

— Courtney Peterson, Ph.D.


Peterson mentioned that percentiles are problematic because they change over time and can become outdated. However, she emphasizes that, even if BMI percentiles were updated to be as accurate as TMI for diagnosing adolescents as lean versus overweight, TMI still inherently estimates levels of body fat in adolescents more accurately than BMI does, while also eliminating the need for complicated percentiles.

“These findings are important,” Peterson said. “Many school districts send home report cards labeling adolescents as overweight, and children and adolescents tend to be more vulnerable to weight bias and fat shaming than adults.”

Obesity increases the risk of several chronic diseases in adults, including diabetes, cardiovascular disease and cancer. Children who are overweight are at an even higher risk than adults, and nearly one in six children in the United States is overweight. Several national and global initiatives are underway to screen and diagnose children who are overweight as a first step in curbing the obesity epidemic and the chronic diseases that follow.

Investigators agree that further research is needed to assess the effectiveness of TMI in broader audiences, including wider age ranges and ethnicities.

“We look forward to collaborating with other existing national and global health organizations to analyze additional data for diagnosing weight status among children and adolescents,” Peterson said. “Ultimately, we hope this research lays the foundation for improving the health of adolescents, and we think that down the road TMI will likely replace BMI for children and adolescents.”

Source: University of Alabama at Birmingham


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