No-one wants to hear that they are responsible for their own ill health, or that they are destroying the prospects for their own future. Thus, human nature being what it is in this era of cheap calories, there exists a thriving cottage industry based upon telling people that their excess weight is just fine and can be managed in such a way as to cause no harm. Unfortunately, that just isn't the case. Carrying excess visceral fat tissue does cause considerable personal harm: it reduces life expectancy, significantly increases risk of disease, and for all intents and purposes essentially accelerates the downward spiral of degenerative aging. You won't just be less healthy, you'll also spend more on medical services despite living a shorter life. The amount and quality of evidence that exists to support these conclusions is very hard to argue with. Nonetheless, people try, Canute against the tide.
The visceral fat tissue packed around internal organs is metabolically active, and by this point I think most people are at least passingly familiar with the idea that too much fat tissue distorts the operation of metabolism in ways that lead to metabolic syndrome and type 2 diabetes. These conditions are harmful enough over the long term that scientists have long used diabetes as a stand-in for aging in laboratory animals, a way to induce most of the consequences and conditions of aging more rapidly and thus more cheaply. In our species, type 2 diabetes is a self-inflicted condition for the vast majority of those who suffer it, caused by being overweight. It can even be turned back simply through the exercise of will power, through losing weight via a low calorie diet. It is amazing that this isn't the first thing done by every patient, rather than suffering through years of disability and medications with significant side-effects.
An excessive amount of fat tissue causes many other issues, however. It spurs chronic inflammation through its interactions with the immune system, and inflammation drives all of the common age-related diseases, especially those related to the decline in function and structure of the cardiovascular system. Excess weight also contributes to the development of hypertension, increased blood pressure, which puts further stress on blood vessels and heart tissue. Raised blood pressure is an important determinant of age-related mortality. Fat tissue also clearly drives the corrosion of the mind, as conditions such as Alzheimer's disease are strongly correlated with weight. Some of these links are mediated through the increased levels of cellular senescence produced by the presence of visceral fat tissue - recall that senescent cells are one of the root causes of aging, and more of them is a bad thing. Along the same lines, fat tissue and its activities can be linked to dysfunction of the immune system. It is just a really bad idea to get fat or stay fat: you are damaging yourself in so many ways.
The idea that people can be fat but medically fit is a myth. Early work, as yet unpublished, involved looking at the GP records of 3.5 million people in the UK. The researchers say people who were obese but who had no initial signs of heart disease, diabetes or high cholesterol were not protected from ill health in later life, contradicting previous research. A summary of their study was discussed at the European Congress on Obesity.
The term "fat but fit" refers to the alluring theory that if people are obese but all their other metabolic factors such as blood pressure and blood sugar are within recommended limits then the extra weight will not be harmful. In this study, researchers analysed data of millions of British patients between 1995 and 2015 to see if this claim held true. They tracked people who were obese at the start of the study, defined as people with a body mass index (BMI) of 30 or more, who had no evidence of heart disease, high blood pressure, high cholesterol or diabetes at this point. They found these people who were obese but "metabolically healthy" were at higher risk of developing heart disease, strokes and heart failure than people of normal weight.
Several studies in the past have suggested that the idea of "metabolically healthy" obese individuals is an illusion, but they have been smaller than this one. The new study involved 3.5 million people, approximately 61,000 of whom developed coronary heart disease. The scientists examined electronic health records from 1995 to 2015 in the Health Improvement Network - a large UK general practice database. They found records for 3.5 million people who were free of coronary heart disease at the starting point of the study and divided them into groups according to their BMI and whether they had diabetes, high blood pressure (hypertension), and abnormal blood fats (hyperlipidemia), which are all classed as metabolic abnormalities. Anyone who had none of those was classed as "metabolically healthy obese".
The study found that those obese individuals who appeared healthy in fact had a 50% higher risk of coronary heart disease than people who were of normal weight. They had a 7% increased risk of cerebrovascular disease - problems affecting the blood supply to the brain - which can cause a stroke, and double the risk of heart failure. While BMI results for particular individuals could be misleading, the study showed that on a population level, the idea that large numbers of people can be obese and yet metabolically healthy and at no risk of heart disease was wrong. "So-called metabolically healthy obesity is not a harmless condition and perhaps it is better not to use this term to describe an obese person, regardless of how many metabolic complications they have."