The research results here are from the latest in a line of epidemiological studies to firmly refute the obesity paradox, burying it with more data and better study design, to show that excess weight is very definitely harmful to health and longevity. The obesity paradox was the idea that excess weight - meaning excess fat tissue - could be protective in some circumstances in older individuals, such as in the case of cardiovascular disease. It arose from the combination of (a) flawed study design and (b) human nature. There are a lot of overweight and obese individuals in the world today because technological progress has greatly reduced the cost of calories. As a result more people consume significantly more calories than was the case in even comparatively recent history, and that has the natural consequence of excess fat tissue. People who are overweight, just like all other individuals, tend to want to hear comforting things about their present state. Hard truths are called hard truths for a reason. Thus the incorrect research results, while being widely attacked and then debunked within the scientific community, nonetheless received a great deal of attention from the public at large simply because they said what people wanted to hear.
Unfortunately, excess visceral fat tissue is harmful. The more of that fat tissue carried and the longer it is carried, the greater the negative impact on risk of age-related disease, quality of life, and life span. The more fat tissue, the greater the lifetime medical expense, even as the expected length of life is shorter. Stepping away from epidemiology, the recording of outcomes, to look at the biochemistry of fat tissue, it becomes ever more clear that it would be highly counterintuitive for any overall health benefit to derive from a large amount of visceral fat. Fat tissue generates chronic inflammation through a variety of mechanisms, including generation of senescent cells, and in this way directly accelerates many of the aspects of aging.
How did the original studies - those finding excess weight to be protective - arrive at the incorrect conclusion? Primarily, the researchers failed to account for the weight loss that tends to occur in the more severe stages of age-related disease. Older people who are thin fall into two camps. The first camp have been thin their whole lives, and are comparatively healthy. The second camp have been overweight for much of their lives, and have only recently lost that weight due to the progression of illness. They are comparatively unhealthy and experience higher mortality rates. Without separating out these groups, the ill, thin people greatly distort the overall picture of weight in later life. The open access paper here adds another mechanism that can help to explain the issue, in that obese and overweight individuals appear to be diagnosed with heart disease at earlier stages than is the case for thin people. This breaks some of the assumptions baked into earlier studies regarding duration of illness and time to mortality.
Obese people live shorter lives and have a greater proportion of life with cardiovascular disease, reports a new study. The study examined individual level data from 190,672 in-person examinations across 10 large prospective cohorts with an aggregate of 3.2 million years of follow-up. The study shows similar longevity between normal weight and overweight (but not obese) people, but a higher risk for those who are overweight of developing cardiovascular disease during their lifespan and more years spent with cardiovascular disease. This is the first study to provide a lifespan perspective on the risks of developing cardiovascular disease and dying after a diagnosis of cardiovascular disease for normal weight, overweight and obese individuals.
"The obesity paradox caused a lot of confusion and potential damage because we know there are cardiovascular and non-cardiovascular risks associated with obesity, I get a lot of patients who ask, 'Why do I need to lose weight, if research says I'm going to live longer?' I tell them losing weight doesn't just reduce the risk of developing heart disease, but other diseases like cancer. Our data show you will live longer and healthier at a normal weight."
The likelihood of having a stroke, heart attack, heart failure or cardiovascular death in overweight middle-aged men 40 to 59 years old was 21 percent higher than in normal weight men. The odds were 32 percent higher in overweight women than normal weight women. The likelihood of having a stroke, heart attack, heart failure or cardiovascular death in obese middle-aged men 40 to 59 years old was 67 percent higher than in normal weight men. The odds were 85 percent higher in obese women than normal weight women. Normal weight middle-aged men also lived 1.9 years longer than obese men and six years longer than morbidly obese. Normal weight men had similar longevity to overweight men. Normal weight middle-aged women lived 1.4 years longer than overweight women, 3.4 years longer than obese women and six years longer than morbidly obese women.
Overweight and obesity are highly prevalent in the United States, have increased dramatically over the past 3 decades, and affect approximately 2.1 billion adults worldwide. In recent years, controversy about the health implications of overweight status has grown, given findings of similar or lower all-cause mortality rates in overweight compared with normal-weight groups. However, current studies have not taken into account the age at onset and duration of cardiovascular disease (CVD), limiting the ability to account for proportion of life lived with CVD morbidity in individuals who are overweight and obese compared with normal weight. This is especially important because disease burden associated with development of CVD results in less healthful years of life, poorer quality of life, and increased health care expenditures.
In this large study of US adults free of clinical CVD at baseline, lifetime risk for incident CVD was high for all adults and was greater in adults who were overweight and obese. Adults who were obese had an earlier onset of incident CVD, a greater proportion of life lived with CVD morbidity (unhealthy life years), and shorter overall survival compared with adults with normal body mass index (BMI). In addition, the proportion of adults with incident CVD events (compared with non-CVD death) was significantly higher in adults who were overweight or obese compared with adults in the normal BMI group. Overweight and obesity were associated with increased hazards of incident CVD event after adjustment for competing risks of non-CVD death across all index age ranges.
While health hazards of obesity have long been recognized, recent studies have spurred controversy about the specific relationship between overweight status and mortality. Among these prior analyses, measurement bias may be present owing to inclusion of self-reported height and weight data. Further, inclusion of participants with comorbidities at baseline, specifically prevalent CVD, may contribute to selection and survival bias because of protopathic bias (reverse causation) related to unintentional weight loss. In our study, we were able to leverage long-term follow-up in a large group of adults free of CVD at baseline to estimate risk of incident CVD and associated CVD morbidity (unhealthy years lived with CVD). While we do observe evidence of the well-described overweight and obesity paradox, in which heavier individuals appear to live longer on average after diagnosis of CVD compared with individuals with normal BMI, our data when following up individuals prior to the onset of CVD indicate that this occurs because of a trend toward earlier onset of disease in individuals who are overweight and obese. This false reassurance is akin to the phenomenon of lead-time bias observed in other situations, such as with cancer screening.