It’s one of those eternal questions for which experience seems to suggest anecdotal “truth.” Ask a group of men and women who they think loses fat the most easily, and what you might not get in consensus you’ll get in vehemence. (What’s your guess?) Whatever our experience implies, what does science say? Does metabolism operate differently in the genders? What’s the story with varying body composition? Finally, are there behavioral or motivational patterns in the weight loss experience that appear to differ – as a whole – between men and women? While our individual distinctions may well trump gender based tendencies, understanding common physiological and social patterns can be one more tool to bring to our journeys as we explore what strategies work best for us and what attitudes or approaches we might better apply for success.
The Body Composition Perspective
Around the age when puberty hits, males and females appear to follow distinctly different paths towards typical body composition. We know this pattern is associated with measurable differences in dominant steroid sex hormones among other things. Whatever happens with hormones, the resulting difference leaves men with more skeletal muscle on average and lower body fat as a percentage of total weight. This is the part that many women have told me is straight-up unfair. I agree. Muscle is wonderful. It’s associated with healthier aging, strength, balance, and metabolic power. This said, muscle is not a strictly male birthright. Men aren’t immune to significant fat gain and muscle loss. Women, with proper protein intake as well as strategic effort, can build and maintain healthy muscle mass that affords them the same metabolic and age-related benefits that men enjoy.
The fact is, both genders are capable of carrying 30-100 billion adipocytes (fat cells). When we assess men or women for body composition, it’s a non-gender-based way of comparing how much fat and non-fat is there. Once a fat cell develops, it stays unless it’s lipo-suctioned out. (FYI: fat cells can grow in both size and number regardless of gender). These billions of fat cells represent our biggest energy reserve no matter how lean we are. If a person is 175 pounds and 25% body fat, this reserve represents over 150,000 calories! The trick is mobilizing it and actually using it as fuel to perform work.
Men, with their (usually) larger mass of lean tissue tend to carry the ability to use fat for fuel at a higher rate (absolute calories per day or per hour), while women typically have slightly slower metabolic rates, thus burning through their (generally larger) reserve at a slower pace. Having less muscle mass – whether you’re male or female – means you also have a smaller capacity to store glycogen as well. Essentially, having less muscle is like operating with a much lower carbohydrate tolerance, unless your daily activity significantly depletes glycogen stores (which usually takes north of 90 minutes per day of rather high-intensity training). Frustrating, yes?
A silver lining for women is their tendency to NOT store visceral adipose tissue (VAT) as readily as men do. That means women carry more fat subcutaneously (beneath the skin) on the lower half of the body, whereas men tend to store it in what’s called the “android” pattern and end up with more fat deposits within the abdominal cavity (in and amongst the organs). Storing VAT in that “apple shaped” configuration is considerably unhealthier than storing weight in the lower “pear shaped” half.
Despite men's greater tendency to store VAT, researchers have observed that men have an easier time losing VAT in a few weight loss trials using calorie restriction, where women displayed more fat loss from subcutaneous stores. Perhaps it’s simply a matter of men having more VAT to lose? Other investigations haven’t displayed such clear gender benefits for men but suggest partial carbohydrate restriction (to 40% of total calories rather than the research standard of 65% carb) with higher protein intake facilitated near-equal weight loss in both men and women over the course of a year. That said, this work revealed that men and women lost the same percentage of weight from beginning to end, but the men saw greater reductions in body fat % and had better lean body mass maintenance than women. Interestingly, this study failed to incorporate resistance training. (They used walking 30 minutes 5 days per week as the activity.) It also didn’t use drastic caloric restriction: women ate 1700 calories, and men ate 1900 calories. In the end, it seemed the dietary balance had more to do with fat loss than gender did: both males and females on the highest protein plan (moderately-reduced carbs) had the most success with losing weight and fat. Additionally, a meta-analysis of gender and weight loss comparisons revealed that men and women will both lose considerable lean mass on diet-only (calorie deficit) weight loss efforts, but both genders can safeguard themselves from muscle loss somewhat if they incorporate frequent strength training.
The moral of this story? Both women and men can lose weight and body fat effectively with proper fitness and nutritional strategy. This process doesn’t require a drastically different approach specific to gender, but it will most likely require more patience from women. The take-home conclusions from the research suggest that both men and women ought to get adequate protein (maybe even double the RDA) and lift weights in addition to walking regularly to be successful with weight loss and fat loss attempts. Additionally, there are bound to be better studies in the pipeline on this subject. To date, females have been short-changed when it comes to their inclusion in this type of research.
Biological Differences in Metabolism
We already recognized that men and women both have a huge ‘"fuel reserve," and I may have made it appear that men have an easier time burning more fat than women, which means this next part may get a bit confusing. We all store some fat in our muscle called intra-muscular triglycerides (IMTG), some in our liver as triglycerides and some in body fat also housed in triglyceride form. Women store slightly more intra-muscular triglycerides than men (up to 2000-3000 calories worth), but females store less glycogen than men (usually around 1200 calories to the guys’ 1500-2000 calories, depending on muscle mass). Women also have higher concentrations of transport proteins in skeletal muscle tissue.
In the big picture, women appear to be better at mobilizing fat – meaning they can more easily release it from the spaces it’s stored and make it available for complete oxidation (fat burning). The mobilization of fat is regulated by two key enzymes: 1) hormone-sensitive lipase (HSL), which is located in each fat cell and triggers the release of triglycerides as free fatty acids (FFA) into circulation and 2) lipoprotein lipase (LPL), which is located throughout the blood vessels and acts to break apart triglycerides floating through the blood to make the fatty acids available for energy by working cells or more likely make FFAs available for storage in fat cells. Women have higher concentrations of LPL in their legs and hips, which may account for the ease in which they store fat in those areas compared to men. Contrary to anecdotal opinion, the fat deposits in the abdomen (as opposed to legs or hips) are more sensitive to HSL in both men and women due to the abundance of the type of receptors that tend to be triggered by HSL in abdominal fat stores.
Epinephrine (a.k.a adrenaline) is the main signal that throws HSL into gear to allow the release of FFAs into the bloodstream. Epinephrine is most beneficial for fat use purposes during aerobic exercise. People who are well-trained aerobically are very sensitive to the epinephrine-HSL-fat release sequence. Unfortunately, obese individuals seem to have a muted or blunted response and may require considerably more epinephrine and/or aerobic training time before they can "release" the contents of their fat cells. In a bit of frustrating irony, despite having a larger energy reserve, obese individuals have a harder time accessing it. Further, individuals with poor protein status may face challenges transporting fatty acids to the cells that can metabolize them because FFAs must be carried through the blood by proteins – mostly albumin.
Interestingly, estrogen (more abundant in females) has been shown to inhibit LPL (whether the LPL is helping with storage or release of FFAs), which makes it seem like this female hormone indeed makes for more “stubborn” lower body fat. At the same time, estrogen also enhances epinephrine production and stimulates growth hormone, both of which mobilize fatty acids but to some degree block glucose uptake by active tissues. Huh? The influence of estrogen mostly enhances fat mobilization during activity and preserves glycogen, and this has been shown to be a significant gender difference when measuring Respiratory Exchange Ratios (or Respiratory Quotients) in exercising individuals. Women appear to rely more heavily on intra-muscular triglycerides for energy across a variety of intensities and have a tough time depleting glycogen stores. In other words, women tend to spend their limited glycogen stores more conservatively than men during activity.
The same is not true at rest, however. When researchers adjust for gender differences in lean mass, it appears women burn less fat at rest than men. So, despite mobilizing and burning slightly more fat during activity than men, women revert to burning other sources of fuel (otherwise understood as more glucose) more quickly at rest. In the end, it seems women need to put forth more effort than men to burn more absolute amounts of fat despite having sharper fat-utilization skills.
On top of the biochemical challenges, women face research and associated marketing bias. Most exercise and performance nutrition research is conducted using young, trained, fit male athletes. The 4:1 carb to protein ratio promoted as the optimal recovery ratio for exercising individuals may completely un-do women’s efforts to lose fat, since women rarely deplete glycogen stores as deeply as men. The abundance of sugar in such recovery strategies would amount to far more fat storage than the amount of IMTGs and FFAs burned by the average workout.
How can women level the playing field? First and foremost, commit to a regular and rigorous strength training program to build and maintain as much lean tissue as you can. Second, out-walk your male counterparts because as long as you’re walking you’re probably burning fat better than they are. Finally (when you’re ready for it), incorporate some higher intensity intervals into your training regimen!
Behavioral and Motivational Patterns
Finally, it appears that gender patterns exist even when it comes to the behavioral and motivational aspects of weight loss. The difference, research suggests, is how men and women tend to engage weight loss programs. When experts examine how both genders use popular online tools to help them lose weight, for example, they’ve found this engagement is mostly dominated by women, even though more men in North America are more overweight or obese. A higher percentage of women (not just sheer number of females) also tend to use online forums and discussion boards as a major support strategy. It’s important to note that using some sort of tracking tool – an exercise or food journal – is an independent predictor for weight loss success. Though weight loss works through biological mechanisms, the real power behind it is in our behavioral choices themselves. In that regard, effective fat loss is anyone’s game.
Thanks for reading, everyone. Does the above research match your assumptions or experience? What questions or thoughts do you have regarding gender and the weight loss journey?
Written by Paul Kriegler - Corporate Registered Dietitian
This article is not intended for the treatment or prevention of disease, nor as a substitute for medical treatment, nor as an alternative to medical advice. Use of recommendations in this and other articles is at the choice and risk of the reader.