A recent open access paper points to changing cytokine levels as a candidate mechanism for a range of conditions that occur with age and are generally made either worse or more likely by the presence of excess fat tissue. The link between being overweight and a higher risk of suffering the common age-related conditions is well known; chronic inflammation is thought to be an important mechanism here due to the way in which it impacts so many different systems in our biology, but the exact details are still open to debate.
An inevitable consequence of human and rodent aging is sarcopenia - loss of muscle mass. Some muscle loss is due to physical inactivity, but even highly trained athletes lose muscle mass and strength with age. Although exercise programs can prevent and/or ameliorate sarcopenia, the effectiveness of exercise interventions to build muscle and effect metabolic improvements is less efficient in elderly subjects than in the young, due to multiple cellular and biochemical changes. ... Adipose tissue gain also is very common in aging and is a growing health concern for all ages. Visceral (abdominal) fat is of the greatest health concern because it is associated with insulin resistance, type 2 diabetes, cardiovascular disease, dementia, cancer, and overall mortality. ... Furthermore, obesity prevents muscle gain in response to functional overload [and] the combination of obesity and sarcopenia (so-called sarcopenic obesity) carries high health risks.
Another hallmark of aging is declining adaptive immunity, with complex alterations in innate immunity. Immune senescence is associated with mortality from all causes, including infectious diseases. Natural killer (NK) lymphocytes are innate immune cells that control intracellular infectious agents and cancers. In contrast to T and B lymphocytes, NK cell number is relatively increased in healthy aging and defects in NK cell function are subtle. However, declining NK cell number or function in aging is associated with death in the elderly. Therefore, mechanisms that preserve NK cell number and function may promote healthy aging.
To relate sarcopenia, obesity, and declining immunity in aging, we speculated that these conditions are linked processes, which are controlled by adipose tissue-derived and skeletal muscle-derived cytokines, known as adipokines and myokines, respectively
You can't really control the degree to which your immune system has been and will be hammered by various common herpesviruses, such as the near-omnipresent cytomegalovirus, but do you have a great deal of control over the fat tissue end of the relationship proposed in this paper. Letting yourself go to seed, getting fat and unfit, has consequences in the long term: a shorter, less healthy life with higher medical bills. Maybe science and those medical costs will dig you out of this hole before it kills you, but why roll those dice if you don't have to? The future of aging, health, and the biotechnologies of rejuvenation on the horizon is already uncertain enough for those of us in middle age today. Every extra year you can gain might make the difference between taking advantage of the first therapies to reverse aging and missing that boat entirely.