Quick answer: Much of mainstream diet and exercise advice was developed on studies of men and simply applied to women — but female physiology changes across puberty, the menstrual cycle, pregnancy and perimenopause in ways that affect sleep, mood, metabolism and cardiovascular risk. For many women in their 40s and 50s, the fix for ‘what used to work no longer works’ isn’t eating less and training harder — it’s better sleep, more fuelling (not less), and strength training.
Originally written in May 2026.
Approaching 48 with a wife marginally younger, a lot of the talk in our friendship group when health related concerns middle-life issues, and at the moment peri-menopause and menopause are commonplace. It’s interesting also how many women present to my heart clinic with symptoms that actually are often hormone related rather than cardiac. I expect it’s no coincidence that at my current age i’m far more switched on to that that I ever used to be. I’m still learning though, as Cardiologists aren’t trained in Gynaecology or family-medicine (although in my opinion they really should be!). I’m always keen therefore to hear from experts in that field, and last week I listened to a long-form interview with Dr Stacy Sims, the exercise physiologist and nutrition scientist best known for the phrase: “Women are not small men.” It is a deliberately memorable line, but behind it is an important point. A great deal of medical, nutritional and exercise science has historically been based on studies in men, with the findings then generalised to women.
That matters because women are not simply smaller versions of men. Female physiology differs across puberty, the menstrual cycle, pregnancy, hormonal contraception, perimenopause, menopause and ageing. Hormones affect far more than reproduction. They influence sleep, mood, body composition, inflammation, muscle, bone, metabolism, appetite, and cardiovascular risk.
Why does what used to work stop working in midlife?
One of the strongest themes in the interview was the experience many women describe in their 40s and 50s: “What used to work no longer works.” A woman who has kept fit for years, eaten carefully, perhaps run regularly or done classes, suddenly finds herself gaining weight, sleeping badly, feeling more anxious, recovering less well, or developing aches, pains and soft-tissue injuries. This basically describes my wife and many of my female friends currently. The understandable response is often to do more of the same: eat less, train harder, add more cardio, skip breakfast, or try intermittent fasting.
Dr Sims’ argument is that, for many women, this is exactly the wrong direction of travel. During perimenopause, hormone levels do not simply decline smoothly. They fluctuate unpredictably. Oestrogen and progesterone affect multiple systems, and changes in these hormones can be associated with poorer sleep, changes in gut microbiome diversity, more inflammation, increased visceral fat storage, reduced muscle power, and altered glucose handling. This does not mean women are doomed to decline, but it does mean the strategy often needs to change.
Should women eat less to lose weight in midlife?
A key message was that women in midlife often need to fuel better, not less. This is one of the more counter-cultural parts of the discussion. Many women have grown up in an era of diet culture, where the default answer to weight gain is calorie restriction. But if the body is already stressed, sleeping badly, under-recovered and being asked to exercise hard, then under-fuelling may worsen the problem.
Dr Sims is particularly critical of the idea that women should routinely delay food until late morning, especially if they are exercising early. Her view is that women generally do better when they eat earlier in the day, take in some nutrition before training, and avoid relying on fasted exercise as a fat-loss tool. She argues that the overnight fast is usually enough: finish dinner a few hours before bed, sleep, then eat within a reasonable time after waking.
The practical version is not complicated. It does not require obsessive tracking or expensive products. It means trying to have protein and fibre at every meal (something I would encourage everyone to do, regardless of gender, although I certainly don’t hit this 100% myself), eating enough earlier in the day, and avoiding the pattern of coffee, stress, exercise, no breakfast, a rushed lunch, and then cravings or loss of control later in the afternoon.
Why does sleep matter so much in perimenopause?
Sleep was another major theme. Poor sleep is not just unpleasant; it affects appetite, insulin sensitivity, mood, recovery, inflammation and body composition. If a woman in perimenopause is sleeping badly, exercising hard, eating too little and feeling stressed, it is not surprising that her body may resist change. I would probably go further and suggest that sleep is so fundamental as to trump all else. I normally sleep a lot, but on this bank holiday weekend I have basked in even more hours of delicious slumber, and feel amazing for it!
From a medical perspective, I think Dr Sim’s approach is a useful framework. However we should be careful not to overstate things: not every woman responds badly to intermittent fasting, and some women with obesity or metabolic disease may benefit from time-restricted eating if it is done sensibly. The broader point is important though. For many active women, particularly in midlife, the problem is not lack of discipline. It may be a mismatch between what the body needs and what diet culture has taught them to do.
There is also a wider lesson here for healthcare. Women’s symptoms in midlife are too often dismissed as vague, emotional or inevitable. Perimenopause can present with sleep disturbance, anxiety, palpitations, body composition change, tendon problems, fatigue, brain fog and loss of confidence. Of course, not everything should be attributed to hormones — blood pressure, cholesterol, thyroid function, iron status, vitamin D, diabetes risk and cardiovascular symptoms still need proper assessment for example, but nor should we pretend that hormonal transition is irrelevant.
The most useful takeaway for this week is simple: if you are a woman in your 40s or 50s and what used to work no longer works, the answer may not be to punish yourself with less food and more cardio. It may be to step back and rebuild the foundations: sleep, adequate fuelling, protein, fibre, strength, recovery and consistency.
This is not about becoming fragile or fearful. It is the opposite. It is about understanding the physiology, adapting intelligently, and training for health, strength and function rather than simply chasing weight loss. So to summarise, have a think about these actionable takeaways:
- Do not assume eating less is always the answer.
In midlife, under-fuelling can worsen fatigue, cravings, poor recovery and stress. - Eat earlier in the day.
Especially if exercising in the morning, consider taking in at least a small amount of protein, and possibly carbohydrate depending on the session. - Prioritise protein and fibre.
Aim to include both at every meal or snack where possible. - Use the overnight fast naturally.
Finishing dinner a few hours before bed and eating breakfast the next morning may be more physiologically sensible than skipping food until late morning. - Take symptoms seriously.
Sleep change, anxiety, palpitations, tendon pain, weight change and fatigue may all deserve proper assessment rather than dismissal.