At the same height and weight, a man and a woman are not carrying the same body. On average a woman has around 10 percentage points more body fat than a man at the same BMI, and she stores it in a different place. That difference shapes how weight goes on, where it settles, what it does to health, and how it comes off. Most people find out about it only when their own body starts changing the rules in midlife.

At Anova we see couples, siblings and colleagues compare notes and come away confused, sometimes discouraged. Same food, same walks, very different results. Much of that comes down to biology that nobody explained.

Where the weight goes

Men tend to store extra fat around the middle and inside the abdomen, packed around the organs. This is visceral fat, and it is the metabolically active, inflammatory kind most linked with type 2 diabetes, fatty liver and heart disease. At comparable levels of body fat, men carry more of it.

Women before menopause tend to store more fat under the skin of the hips, bottom and thighs. This lower-body fat is, on balance, protective. Research on adipose tissue links fat stored around the hips and thighs with lower metabolic risk, and premenopausal women typically have better cholesterol and triglyceride profiles than men of the same age. Women’s fat tissue also takes up roughly twice the share of circulating fatty acids after a meal (about 8% versus 4% in one set of measurements), which helps keep those fats out of the liver and muscle.

So a man and a woman can both “need to lose 10 kilograms” and be in quite different places on risk. A man’s waistline is often the more urgent number. It is also why a scale reading alone tells you less than a tape measure does (why fat cell size matters more than weight).

The pattern is not fixed by sex alone. Around 40% of women store fat mainly around the abdomen, and when they do, their metabolic risk looks much more like a man’s.

The hormones doing the steering

Oestrogen is a large part of why women store fat lower down, and why it behaves differently when it is there. Testosterone does much of the steering in men: it supports muscle, which burns more energy at rest, and it tends to restrain the build-up of visceral fat.

What surprises most men is that the relationship runs in both directions. Lower testosterone makes it easier to gain fat around the middle. Fat tissue, in turn, converts testosterone into oestrogen, which signals the brain to make less testosterone. More belly fat, less testosterone, more belly fat. A 2013 review of 24 studies found that weight loss reliably raised testosterone in men with obesity, and that how much weight a man lost was the best predictor of how much his testosterone recovered.

What falling testosterone does to drive

Testosterone falls gradually with age, and faster with weight gain, poor sleep and chronic stress. Its effect on weight is not only about muscle and fat.

Men with low testosterone commonly describe flat energy, lower drive, and less appetite for the things that used to feel rewarding, including exercise. There is a plausible mechanism. In animal studies, testosterone increases voluntary physical activity through the brain’s dopamine pathways, the same reward circuitry that makes effort feel worth it. We should be careful not to over-read mouse data, but it matches how many men describe it: the gym did not get harder, it got less satisfying.

At Anova we think that changes how the plan should be built. A man who has lost his drive to train usually has plenty of willpower. He may be in a loop where the weight is lowering the hormone that made movement feel good. Breaking the loop usually starts with the weight and the sleep, not with forcing more workouts. The kind of exercise matters too: shorter, harder sessions and strength work do more for body composition than long steady cardio (why intensity beats duration).

Low energy and low drive have many causes, so this is a conversation for a GP, not a self-diagnosis. Men are also the group least likely to have that conversation. More than 1 in 5 Australian men don’t see a GP in a given year (what that changes about care).

Menopause changes the rules

For women, the transition through menopause is the biggest shift in weight biology since puberty. Australian women reach menopause at around 51 on average, and the years leading up to it matter as much as the event itself.

The best long-term data come from the US SWAN study, which followed women through the transition with body-composition scans. Two things stand out:

The rate of fat gain roughly doubles as the menopause transition begins, while lean muscle starts to fall.
The scale often doesn’t show it. Total weight kept rising at much the same pace as before; what changed was the mix, more fat and less muscle. Things settled about two years after the final period.

As oestrogen falls, fat storage also moves from the hips and thighs to the abdomen. Many women describe a body that suddenly “doesn’t feel like mine”, with a new waistline despite an unchanged diet. The scans back them up. The protective pattern of earlier life is giving way to the male pattern, with the risk profile that comes with it.

The practical lesson is to protect muscle early. Resistance training two or three times a week and enough protein across the day are the two levers with the most evidence, and they work best when started before or early in the transition rather than after. Sleep, often disrupted at this stage, is the third (what diet, exercise, sleep and stress each do).

Why men often lose weight faster, and why it isn’t fair to compare

When couples start a plan together, the man often loses weight faster at first, and it is one of the more consistent findings in the research. In a large European trial of more than 2,000 adults on an eight-week low-calorie diet, men lost significantly more weight than women and saw bigger falls in fat mass. Women lost more from their hips and saw different benefits.

Men are, on average, larger, carry more muscle and burn more energy at rest, so the same reduction in food is a bigger relative deficit. Women’s bodies also defend lower-body fat more stubbornly, likely an evolutionary hold-over to protect energy for pregnancy and breastfeeding.

Comparing your progress to your partner’s tells you very little. Waist measurement, strength and how clothes fit are fairer measures than the scale, for both of you.

Who diets, who gets help, and who gets left out

The biology differs, and so does the way men and women come to weight loss.

Women diet more, and start younger. In the long-running US Project EAT study, 56% of teenage girls reported dieting, compared with 23% of boys. By adulthood the figures were 65% and 44%. That matters because repeated dieting in adolescence is itself linked to later weight gain, not loss (why adolescence matters). Many women arrive at midlife with decades of attempts behind them and a body that has learned to defend its weight.

Men try less, and often don’t see the problem. An Australian survey found men were less likely than women to be attempting any form of weight control (47% against 55%), and noted that many men who were already overweight were unconcerned about it. In US national data, men who saw their weight as “about right” when it wasn’t were 71% less likely to want to lose weight than men who saw it accurately.

That is a problem, because men are the larger group at risk. In Australia, 72.5% of men live with overweight or obesity, compared with 61.9% of women.

The weight-loss world has been built mostly for women. Across 244 trials of lifestyle weight-loss programs, participants were on average 73% women. A third of the trials enrolled only women; 5% enrolled only men. Commercial programs, their marketing and their language have followed the same pattern. The result is a field that knows a great deal about helping women lose weight, and much less about reaching men.

When men do join, they tend to stay. A UK review of the evidence on men and weight management found that fewer men sign up, but those who do are less likely than women to drop out. Men preferred programs that were factual, flexible and framed around fitness and health rather than dieting, and run in social settings rather than clinics. The approaches that have worked show it:

a Scottish program run through professional football clubs, where men lost around 5 kg more than a comparison group at 12 months;
an Australian online program for men from the University of Newcastle, whose participants lost close to 10 kg on average.

At Anova we read this as an access problem more than a motivation problem. Men respond well to the right offer; most of what has been offered to them was designed for someone else. Combined with men’s lower contact with GPs, it leaves a large group of people at the highest risk with the least help.

The people you live with move your weight too

Weight is not only individual biology. A US study following young adults found that moving from dating to living together or marrying was linked to a higher chance of developing obesity. Shared meals, shared couches, less time for exercise and the comfort of settling down all play a part. Parenthood adds broken sleep, less time and eating on the run.

It works in the other direction as well. In a trial where one partner joined a structured weight program, about a third of the partners who did nothing at all lost at least 3% of their own body weight in six months, and the two partners’ weight changes tracked each other. Researchers called it the ripple effect.

That is one of the more useful findings in this area. When one person in a household changes the food in the cupboard, the timing of dinner or the after-dinner walk, the whole household tends to move with them.

What to do with this

Measure your waist as well as your weight. For men, the waist is usually the more important number. For women in midlife, a growing waist with a steady scale is a signal to act.
If you are a woman in your 40s, start strength training now, before the transition speeds up muscle loss.
If you are a man with low drive, flat energy and a growing waist, raise it with a GP rather than pushing harder at the gym.
If you are a man who has never tried a structured program, look for one built around fitness and facts, not a diet plan designed for someone else.
Plan as a household. Agree on one change you will both make, and stop comparing your scales.

At Anova we find most frustration about weight comes from measuring yourself against the wrong body. Men and women are working with different equipment. Which part of your body’s own rules have you been fighting, rather than working with?