As an obesity medicine specialist, I often hear variations on this question from my women patients: “My husband and I both struggle with our weight, but when we start a new diet, he always seems to be able to shed the pounds quicker, even though I’m trying just as hard. Is this normal?”
First, let’s acknowledge that losing weight is difficult for almost everyone, including men, and it’s not just a matter of “trying harder,” or simply taking in fewer calories than we expend, because our bodies fight back. The human body has evolved to avoid starvation, which is why most diets don’t work: the metabolism slows, appetite and cravings increase, and a variety of other physiological mechanisms kick in to resist significant and sustained weight loss.
While this is true for anyone who wants to lose a few pounds and keep them off, obesity complicates the picture even further. Obesity is an extremely complex multifactorial disease that is associated with more than 200 medical conditions, and scientists are still working to untangle many of these intertwined, mutually reinforcing associations. But although we don’t yet understand all the factors involved, some of them do have clear connections with differences in male and female biology.
So — to return to the original question — yes, it’s actually a well-documented phenomenon: women often do have a harder time losing weight.
The many-sided role of estrogen
Not surprisingly, sex hormones are likely a significant contributor to this difference. Estrogen, in particular, affects a wide range of physiological processes.
On the positive side of the ledger, estrogen increases energy expenditure, and, through neurobiological pathways in the central nervous system, it also plays a role in suppressing appetite, leading to changes in food intake at different phases of the menstrual cycle. Interestingly, studies have shown that women are more likely to report cravings for sweet foods and men savory foods, and that age, for women but not men, is inversely correlated to cravings for fat and carbohydrates.
Most significant to the issue at hand, though, is estrogen’s contribution to the accumulation of fat in subcutaneous tissue, where it is more likely to be stored long term rather than used for fuel. This means that premenopausal women tend to have a greater percentage of body fat than men, and that this fat is harder to lose. Compounding the impact of body composition, women also typically have less muscle mass, which burns more calories than fat tissue, even at rest.
In contrast, men and postmenopausal women tend to accumulate more visceral fat, which wraps around internal organs. Although visceral fat is more readily used for energy needs — and thus easier to lose — it’s also considered more dangerous, as it is associated with increased risk of both insulin resistance and cardiovascular disease.
Visceral fat expands by adipocyte hypertrophy (the fat cells increase in size), while subcutaneous fat expands by adipocyte hyperplasia (the cells increase in number). Smaller subcutaneous fat cells can store more lipids such as triglycerides. In visceral fat, when the adipose cells reach maximum size and can no longer store more lipids, these lipids are deposited in other tissues, leading to insulin resistance. Visceral fat promotes insulin resistance via other mechanisms as well, such as the secretion of proinflammatory cytokines. The increased inflammation and higher blood lipid levels associated with excess visceral fat also contribute to many other conditions, including atherosclerosis, which can lead to heart attacks and strokes.
The increased health risk posed by visceral fat is the origin of the old rule of thumb about apple-shaped bodies (more belly fat) being more at risk than pear-shaped bodies (more fat in the hips and thighs). In fact, waist circumference is highly correlated with increased risk of type 2 diabetes and cardiometabolic disease. The risk threshold is generally considered to be 35 inches for women and 40 inches for men, with different thresholds for different populations. While people with obesity generally have excess fat in both subcutaneous and visceral tissue, those without metabolic complications often have a larger proportion of subcutaneous fat, especially in the thighs.
Other contributing factors
Genetic factors affect body weight and fat distribution as well, but the sex-specific impact is less well understood. One study, for example, showed that among mice whose sex organs had been removed, those with female sex chromosomes (XX, XXY) gained more body weight than those with male chromosomes (XY, XO), suggesting that sex chromosomes themselves play a role that is separate from the effects of sex hormones. In addition, large-scale genome-wide studies have identified a number of single-nucleotide polymorphisms (variations at a single position in a DNA sequence) associated with fat accumulation or distribution that were either significant in females but not in males or had larger effects in females than in males. These sex-specific differences account for a very small fraction of the genetic heritability of obesity (general body shape and natural “set point” weight range are highly influenced by genetics as well), but they do represent a promising avenue for further study.
Obesity is also affected by an enormous range of additional variables, including lifestyle, other physical and mental health conditions, medications, socioeconomic circumstances, sleep patterns, previous weight-loss experience, social and psychological pressures, and on and on. And while some of these factors may involve sex- or gender-related differences, the collective impact of all the factors is usually more significant than any one dimension.
Personalization is key
For this reason, an effective weight management program needs to take into account all the factors contributing to an individual’s weight gain, and the interactions between them, and provide personalized guidance based on those specific factors. Fortunately, the field of obesity medicine has made great strides in recent years, allowing us to draw on vast quantities of data to identify which combinations of interventions — including diet, physical activity, behavioral modifications, pharmacotherapy, devices, procedures and surgery — are likely to be most successful given an individual’s unique situation.
Losing weight may be hard, but biology isn’t destiny. We have the tools to alter the outcome. For those who want to take that next step, effective treatment options do exist.
