Over the last decade, intermittent fasting has become an increasingly popular diet among people of all ages. But how much do we really know about its long-term effects — and is it safe for women?
Remember the first time you heard a friend or colleague claim to be absolutely starving right before lunch — only to find out they had been ‘fasting’ since dinner the night before? Perhaps you left the conversation perplexed, slightly concerned and, possibly, in awe of their discipline.
Cut to 10 or so years later and this method’s popularity has majorly increased. Practical, easy to fit into working life and generally less restrictive than other diets (no complicated recipes or food groups to avoid), intermittent fasting is praised for benefits far beyond just weight loss.
But a recent study has raised concerns about the diet’s safety, reporting a 135% higher cardiovascular mortality in those who practise it. Some studies also suggest it affects women differently — particularly in older or postmenopausal women, who naturally have higher fat levels.
Given these differences, is it possible for women to practice intermittent fasting safely? Here’s everything you need to know about the diet.
What is intermittent fasting?
A structured eating pattern that focuses on the times you eat, intermittent fasting (IF) involves alternating between ‘fast’ and ‘feast’ days (or eating within a set timeframe). On ‘feast’ days, you eat normally (but healthily), on ‘fast’ days, calorie intake is generally reduced within a set window.
Common fasting patterns include:
- 5:2: Eat normally five days a week, restrict calories two days
- 16:8: Fast for 16 hours, eat within an eight-hour window. Most fasting occurs overnight. For example, eating from 12 pm to 8 pm means skipping breakfast
- Alternate-day fasting: Fast every other day
What are the benefits?
It’s a popular diet for fat loss because after roughly 12 hours of fasting, the body ‘flips the metabolic switch’ and starts burning fat for fuel.
“After this period, the body has used up its glucose stores and starts burning ketones released from fat breakdown,” explains Dr Deborah Lee, Dr Fox Online.
Others see it as a ‘rest’ for the digestive system and a way to feel more in control of eating habits.
For 43-year-old nutritionist Angela Clucas, intermittent fasting was the only thing that helped her adjust to early menopause and HRT. She had been trying to shed some weight and, after trying everything from intense HIIT workouts to macro and high-protein diets, she saw no results until she discovered IF.
Eight months later, she’s lost the weight and seen several other improvements: “I’ve noticed better insulin regulation, I’m feeling lighter and have improved focus in the mornings.”
“Overall, it was a simple way to reduce calorie intake without feeling hungry or restricted.”
According to Dr Lee, benefits can include:
- Improved carbohydrate metabolism and insulin sensitivity (can reverse prediabetes)
- Weight loss
- Improved metabolism
- Lower blood pressure
- Better cholesterol levels
- Reduced chronic inflammation
- Possible improvements in gut microbiome diversity
- Reduced appetite
- Higher energy levels
- Better sleep
- Enhanced concentration
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Is intermittent fasting safe?
When starting out, many people experience short-term side effects like headaches, fatigue, dizziness or irritability — similar to the ‘keto flu’ on low-carb diets, but these usually clear up within a few weeks once the body adjusts.
Initial side effects aside, for adults carrying extra weight, who don’t have eating disorders or other health conditions, IF can be safe and effective. But it’s not without risk — especially if you push too hard.
Most clinical trials have been short and focused only on overweight adults, so the long-term effects remain unclear. One observational study linked an eight-hour eating window to a 90% higher risk of dying from heart disease compared to eating over 12 to 16 hours. But in this study (just as in the one mentioned previously), it’s not clear whether the risk is due to the short eating windows themselves or to other contributing factors.
Longevity expert and co-founder of the Oxford Longevity Project, Leslie Kelly, says this doesn’t necessarily mean fasting is unsafe: “It doesn’t mean fasting directly causes heart problems, but it tells us we should be cautious about very tight eating windows.”
According to Leslie, there could be a few possible explanations:
- Cramming calories into a short window may encourage overeating or less thoughtful food choices, raising cholesterol or inflammation.
- Fasting itself is a physiological stress, which could push the body in the wrong direction for people already at high risk (e.g. with high blood pressure or metabolic syndrome).
- Confounding factors may play a role, so those who fast could also be shift workers or under high stress, both of which independently raise heart disease risk.
For Leslie, the bottom line is clear: “Fasting can be a tool for certain people, but it’s not a one-size-fits-all solution. Extreme fasting windows may be harmful, especially in women or older adults, so moderation and personalisation are key.”
Is IF an effective diet for women?
Women can experience the same cardiovascular and metabolic benefits as men, but hormones make IF more complex.
“Women’s bodies are evolutionarily tuned to sense threats, always checking whether it’s a ‘safe’ time to bring a new life into the world. Fasting can be interpreted as a sign of food scarcity or famine,” says Leslie.
This means the body might perceive fasting as a stressor, which can disrupt hormones, lower oestrogen and progesterone and even affect fertility.
More aggressive approaches, like multi-day fasts, can also trigger missed periods, mood changes or anxiety. One study found fasting reduced DHEA, a hormone important for ovarian function and stress resilience, and it may even raise levels of reverse T3, a thyroid hormone that slows metabolism — making weight loss harder.
Read more: Walking for just 10 minutes after eating could transform your health. Here’s how
On the other hand, practising IF may help women with PCOS by lowering testosterone and insulin levels, which could reduce the risk of type 2 diabetes, high blood pressure and heart disease.
Overall, the evidence is mixed and largely depends on the individual, but for many it can be positive. For Angela, it was life-changing — she believes you just have to make sure you’re being responsible, flexible and adaptable:
“I made sure to hit my daily protein target in other meals, which made them more filling and helped eliminate evening snacking. The key is to view fasting as a tool in the kit, not a rigid rule. For example, if I woke up hungry, I’d wait 30 minutes to see if it passed once I was hydrated. If I’m hungry, I eat.”
How to practice intermittent fasting safely as a woman
The key to fasting safely is to approach it gently and respect your body’s natural rhythms and needs.
As Angela emphasises: “If protein drops too low, you risk losing muscle tissue, which negatively impacts strength and energy.” This is especially important for women over 35 as we naturally start losing muscle at this age.
For those who menstruate, hunger naturally rises at certain points of the cycle. Pushing through it can backfire, leading to lower energy and fatigue, overeating later or a disordered relationship with food — so always listen to your body.
Tips from the experts:
- Adjust other meals to meet nutrient and protein goals to protect muscle
- Sync fasting with the menstrual cycle: it’s easier in the follicular phase (right after your period), but ease off in the luteal phase (the week before your period)
- Start with a 12:12 approach (12 hours eating, 12 hours fasting)
- Some may extend to 14:10, but anything beyond that should be considered carefully
- Avoid extreme fasting (e.g. 18:6) unless under professional guidance
- Drink plenty of water during both eating and non-eating (waking) hours
- Prioritise sleep, hydration and stress management
Read more: Can Ozempic really help with PCOS? Promising link between weight-loss medications and hormonal health revealed
Who shouldn’t fast?
Fasting is not recommended for:
- Anyone pregnant, breastfeeding or trying to conceive
- Anyone underweight or with a history of disordered eating
- Slim women over 60, or anyone at risk of muscle loss
- Children under 12
- Anyone with diabetes or taking medications that require food
- Anyone at risk of nutrient deficiencies or muscle loss
Featue image: Freepik
