Nutritional Pearl

Body Fat May Matter More Than Body Mass Index

Timothy S. Harlan, MD

  • Answer:

    Excess body fat, and not just total weight, could be more dangerous to your health than a number on a scale.

    Six years ago, I shared with readers a study1 that found that even when people’s BMI was within the normal range, if their waist-to-hip ratio was more than 0.9, (the World Health Organization defines this as centrally obese) they were more likely to die of any cause than those whose BMI and waist-to-hip ratio were within clinically normal parameters.

    That study is just 1 indication that how much body fat someone is carrying, as well as where that fat is located on their body, may be a greater indicator of metabolic risk than BMI alone.

    Today’s research, published in the journal Nutrition2 looks more closely at both body fat and specific health risks.

    The Research

    This study2 was carried out in Brazil among nearly 800 men and women who were born in Sao Paolo, Brazil, in 1978 and 1979. Their birth weight was recorded at birth, as well as information regarding their parents. More than 20 years later, the participants were between 23 and 25 years of age and underwent height, weight, and waist measurements as well as skinfold measurements to assess body fat. Blood was drawn for insulin and cholesterol tests, and the participants responded to dietary and lifestyle questionnaires.

    More than 10 years later, the participants were between 37 and 39 years of age. While they again were weighed, measured, and surveyed and provided blood for testing, this time, they underwent a body scan known as air plethysmography that allows much greater accuracy in the measurement of body fat percentage. Another test, dual-energy x-ray absorptiometry, provided measurements of muscle mass and total body weight.

    The researchers classified the participants into 1 of 3 groups:

    1. Healthy Weight (HWI): Those with a BMI in the clinically normal range with a body fat measurement (via skinfold) below the 90th percentile
    2. Normal Weight Obesity (NWO): Those with a BMI in the clinically normal range with a body fat measurement (via skinfold) above the 90th percentile
    3. Overweight/Obesity (OWO): Those with a BMI more than 25 kg/m2, as well as a body fat measurement above the 90th percentile

    For those aged 23 to 25 years, the researchers also analyzed their clinical scores to determine whether they had metabolic syndrome, a collection of metabolic abnormalities that indicates a greater risk of cardiovascular and other metabolic diseases. These abnormalities include:

    1. Waist circumference 90 cm or more for men and 80 cm or more for women
    2. Triglyceride level more than 150 mg/dL
    3. High-density lipoprotein cholesterol level more than 40 mg/dL for men or 50 mg/dL for women
    4. A systolic blood pressure greater than 130 mm Hg or a diastolic blood pressure greater than 85 mm Hg
    5. Fasting blood glucose equal to or greater than 100 mg/dL

    In all cases, if the participants were taking medications for cholesterol or hypertension or insulin-controlling medications, the researchers took that as proof that the participant met the criteria for the abnormality.

    The same information from the participants aged 37 to 39 years was gathered, and the same analysis was performed, and those who were considered to have metabolic syndrome in their 20s were excluded from the final analysis.

    The researchers compared the metabolic syndrome status of the participants in their 30s with their classification by body composition groups (ie, HWI, NWO, and OWO).

    The researchers stated that after considering demographic, dietary, and lifestyle variable, "We did not find differences in the [relative risk] for [metabolic syndrome] between [NWO] and [OWO]."

    What I found interesting about their results is that while those with OWO were 161% more likely to develop metabolic syndrome than those with clinically normal weight status, those with NWO­­––excessive body fat percentage––were 187% more likely to develop metabolic syndrome.

    This pattern of slightly, but perhaps not statistically significant, greater risk for those with   NWO than OWO holds true for the risk of excessive waist circumference, cholesterol levels, and blood glucose levels. Those with OWO were 172% more likely to have hypertension compared with those of clinically normal weight, while those with NWO were 144% more likely to have hypertension.

    What’s the Take Home?

    This suggests to me that excess body fat, and not just total weight, could be more dangerous to your health than a number on a scale. Certainly, this aligns with previous research showing that BMI is inaccurate for those with low body fat, as well as research showing the risks of a higher waist to hip ratio. Here's how to calculate your waist to hip ratio.3

    References:

    1. Harlan TS. Health & nutrition bites. Dr Gourmet. Published online December 2, 2015. Accessed January 11, 2022. https://www.drgourmet.com/bites/2015/120215.shtml
    2. Coelho CCNDS, Bragança MLBM, de Oliveira BR, et al. Incidence of metabolic syndrome in adults with healthy weight, normal weight obesity, and overweight/obesity. Nutrition. 2021;85:111134. https://doi.org/10.1016/j.nut.2020.111134
    3. Harlan TS. Dr Tim says… waist and hip measurements. Dr Gourmet. Published online August 4, 2009. Accessed January 11, 2022. https://www.drgourmet.com/column/dr/032006.shtml