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I recall an obese patient who was referred to a transplant clinic as his stitch wounds hadn't healed after a year. While there's a myriad of side effects caused by immunosuppressive medication after transplants, the usual healing process for patients that underwent the same procedure is around one to two months1.

It's not an isolated example, as patients with very high BMIs can be considered ineligible for transplantation because of the post-surgical complications that follow, namely, delayed wound healing and increased chance of infection. It does not seem to be dependent on diabetes or merely low metabolism rates caused by a sedentary lifestyle (some of the patients perform well in exercise tests and monitor and control their blood glucose levels) and as such, BMI tends to remain the only (imperfect?) factor.

Why does a large percentage of body fat or a high BMI delay or impair healing?

It seems counter-intuitive to me because, as I understand it, the two major parts of the healing process involve 1) a great range of proteins for the creation of new vessels, tissue etc., and 2) The energy needed for the different processes, such as the mitosis of the cells. If blood glucose levels are close to normal and there isn't much of an insulin resistance, then surely it's not a problem of availability for either of the parts to play their role?

Clarification: I restrict the scope of the examples to transplant surgical procedures as what I state is more likely to be factually correct due to personal experience. I would expect wounds other surgical operations to follow the same patterns, but I could be wrong.


[1]: That is an extreme case, especially considering the possibility of effects of diabetes, obesity and steroids compounding. However, there's a general trend.

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It's well known that obese patients have slower wound healing, but the specific cause isn't known; most likely there are multiple causes acting together.

The correlation between obesity and deficient wound healing has long been established. ... Substantial evidence exists demonstrating that obesity is associated with a number of postoperative complications. Specifically in relation to wound healing, explanations include inherent anatomic features of adipose tissue, vascular insufficiencies, cellular and composition modifications, oxidative stress, alterations in immune mediators, and nutritional deficiencies.

--Obesity and Surgical Wound Healing: A Current Review (This is an open-access article that nicely summarizes the open questions)

Obesity has been shown in a number of studies to impair wound healing, and chronic nonhealing wounds in obesity and diabetes are a major cause of limb amputations in the United States. ... Recent evidence indicates that aberrant wound site inflammation may be an underlying cause for delayed healing. Obesity, diabetes, and other conditions such as stress and aging can result in a chronic low-level inflammatory state, thereby potentially affecting wound healing negatively.

--Exercise, Obesity, and Cutaneous Wound Healing: Evidence from Rodent and Human Studies (Also open-access, a little more recent but less wide-ranging)

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