July 18, 2013 | 4 minute read

Should obese people who are metabolically healthy be advised to lose weight?

Risk of type 2 diabetes, heart disease and cancer all increase with excess body fat. Yet research has identified two unique groups: those who are obese but metabolically healthy, and those who are a healthy weight but metabolic unhealthy. This was the topic of a session I especially looked forward to attending at last month’s American Diabetes Association Scientific Sessions.

Metabolic health matters when it comes to cancer. Inflammation and the elevated insulin levels that come with insulin resistance are believed to promote cancer development.

Metabolically healthy obesity (MHO) refers to people who have a body mass index (BMI) of 30 or more (for someone who is 5’6” tall, weight of at least 186 pounds) yet don’t have the metabolic abnormalities that typically accompany obesity. There’s not yet a standard definition for MHO, but usually a person with MHO has no more than one of the following: diabetes, high blood pressure, elevated blood triglycerides or low HDL cholesterol. Studies generally report from 3 to 20 percent of obese people meet criteria to be classified as metabolically healthy.

In some recent studies, people classified as MHO have similar overall mortality rates and deaths due to heart disease as people metabolically healthy and lean. Although in other research, MHO people had double the mortality rate.

A person’s health consequences may depend upon the location of body fat, according to presentations at the ADA meeting.  Excess fat carried in the thighs does not seem to bring the same metabolic consequences as the visceral fat located deep in the abdomen, which often includes fat buildup in the liver.

Several studies presented at the ADA meeting showed that although people with MHO fared better in measures of atherosclerosis, insulin resistance and inflammation compared to other obese people, they were not as healthy as those with normal BMI who were metabolically healthy.  Since these tests are considered early, preclinical signs of disease, the concern is that people with MHO may simply be developing unhealthy consequences of excess body fat more slowly than others. One speaker noted that people with MHO are often younger or have been obese for a shorter time than other obese people.

So the big question is whether metabolic markers of health identify a group of obese people who don’t need to lose weight to protect their health, or whether they may not remain metabolically healthy long-term and should aim to lose at least some amount of excess waistline fat.

In contrast, there are people who are normal weight but have signs of metabolic abnormalities. These people are referred to as Metabolically Obese Normal Weight (MONW) ; for someone 5’6” tall, a weight of 115 to 154 pounds. MONW people have two or more abnormalities regarding blood sugar, blood pressure, and lipids that are usually associated with obesity.  Studies typically show that about 25 percent of people with normal BMI fall in this category, with metabolic abnormalities most common as people get older.

People classified as MONW have greater risk of mortality and diabetes compared to healthy people of normal weight.

For people with MONW, physical activity, including strength-training, may be helpful since this can decrease insulin resistance. Since a normal BMI can include a wide range of weights in some cases of MONW percent body fat may be high and modest weight loss might be recommended to decrease what could be excess body fat for that individual.

Researchers continue efforts to identify the best markers of health, and the most important steps to promote lower risk of heart disease, diabetes and cancer. Meanwhile, it seems we should pay more attention to markers of metabolic health that have been identified, and focus on how our physical activity choices and even small changes in weight or waist may make a difference.

Karen Collins, MS, RDN, CDN, is AICR’s Nutrition Advisor. Karen is a speaker, writer and consultant who specializes in helping people make sense of nutrition news. You can follow her blog, Smart Bytes®, through her website and follower her on Twitter as @KarenCollinsRD.