The most common formula used to assess the risk of obesity is BMI with 25.-29.9kg/m2 considered as overweight and over 30 considered as Obese in the United States and worldwide. Because BMI is an indirect method of assessment, it can overestimate or underestimate the degree of obesity in certain groups such as athletes and elderly. Therefore, it is a good idea to have your BMI accurately measured especially in these group with addition of waist circumference which most obesity specialist, including myself, utilize.
Prevalence of Obesity
Obesity varies greatly by gender, race and socioeconomic status. Stats in the United States found that between 2011-2014, obesity was found in 56% black women and 38% black men; 35% in white women and 34% in white men; 46% in Hispanic women and 40% in Hispanic men and 12% in Asian women and 11% in Asian men.
In those who were under the federal poverty level, it was found to be 39% of the population were obese and in those above the poverty line, the number reduced to 30%. A 2016 study in young children and adolescents concluded that around 17% of children aged 2-19 are obese. Due to increased awareness among the pediatric population, this number among children has leveled off but continues to rise in ages 12-19.
Since 1975, global obesity rates have had a sharp increase in both obesity which again is considered BMI over 30 and in severe obesity which is a BMI crossing greater than 35.
Death Rates by Obesity
A meta-analysis study of 230 cohort studies done by Aune et al. (2016) showed that the lowest risk of obesity after removing confounding factors was around BMI 20-22. These are in non-smokers. But with an increase in BMI by 5 points, the risk went up by 21%.
In overweight (BMI 25-29.9), the median survival time is reduced by 1-2 years.
In class 1 obesity (BMI 30-34.9) this time is reduced by 2-4 years.
In class 3 obesity (BMI > 40) this time is reduced by 8-10 years.
These rates are in same category as smoking and its effects on reduction of survival time. Along with that, early life increases in BMI also play a role in increasing chronic health diseases and mortality. As heart disease is more treatable by medication and intervention, the death rates have not been accurate in predicting mortality and so are determined by development of heart disease.
Coronary Heart Disease
Leading cause of death in the United States is via heart disease at around 24%. Cohort studies show a direct, liner relationship with increasing BMI, increases the risk of heart disease. The risk increases among overweight starting at BMI of 25.
The Million Women Study in United Kingdom followed over 1 million female patients, between ages 55-74 and found the risk of heart disease increased directly as a result of increasing BMI between 20-34, with doubling of the risk at the higher end of the BMI curve. The risks of heart disease tend to be higher in women.
In young adults, a Harvard study between 1922-1935 found the death rate among the teens who were overweight were twice as likely to die from heart disease than their peers.
Heart disease is related to type 2 Diabetes, hypertension, increased triglycerides and cholesterol, increase in body inflammation and sleep apnea.
Ischemic Stroke
Strokes are the fifth leading cause of death in the United States. The studies showed that being overweight and obese are important factors for ischemic stroke but a relationship with hemorrhagic stroke was not established.
Hypertension
Approximately 30% of adults in the United States suffer from high blood pressure with only 50% having a good control. High blood pressure not only increases the risk of heart disease and stroke, but also heart failure. Studies observed that even within a normal range BMI, the blood pressure rises steadily. However, with every 1 unit rise in BMI the risk increased to 12%.
For individuals who are considered overweight at age 18, the risk of hypertension doubled over later adulthood. Adult weight gain of 1kg increases the risk by at least 5%. An all-male Physicians' Health Study followed 13,000 men for 14 years and observed increased risk of hypertension starting from BMI 22-23 compared to those with lesser BMI. It found increasing risk of hypertension with increasing BMI from overweight to obese (BMI over 30). Same applied to women that were observed with their risk being higher with BMI greater than 30 or obesity, compared to men.
Diabetes
As the incidence of Type 2 Diabetes has risen, it has become the 7th leading cause of death in the United States. It leads to chronic inflammation, insulin resistance and cell stress. The risk of diabetes is not just higher in obese men and women but also with those whose BMI is at the upper end of the normal range (BMI 20-24.9) as there exists a strong linear relationship. In a meta-analysis study performed in 2009, the risk for type 2 diabetes doubled in men and women who went from an overweight BMI to obesity (BMI over 30). This risk found in a nurse's study tends to begin when BMI is around 21-22.9 kg/m2. Weight gain is a strong factor strongly associated with the risk of developing diabetes.
In a Harvard/University of Pennsylvania study of male alumni, those with initially low BMI less than 21 early in adulthood, an increase in BMI of 1.5units over a decade nearly doubled the risk of diabetes.
Independent of weight, location of adiposity has an important role in the development of type 2 Diabetes. In women who have a large waist circumference (36.2 inches) were more than 5 times more likely to develop type 2 diabetes, regardless of BMI. As the waist to hip ratio increased, with obesity it caused a linear relationship with increase in type 2 diabetes. Similar, results are found in men. Evidence is clear that early onset weight gain in life, can have an important impact in increasing the risk of type 2 diabetes as an adult.
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