Reverse Health Intermittent Fasting Explained

Reverse Health intermittent fasting is a structured eating approach designed for women over 40, combining defined fasting windows with nutritional guidance tailored to perimenopause and menopause. As interest in intermittent fasting grows across the UK, many women are exploring whether programmes like Reverse Health offer a safe and effective route to weight management and improved metabolic health. This article explains how the programme works, what the evidence shows, which safety considerations apply, and how to get started responsibly within UK clinical guidance.

What is Reverse Health intermittent fasting and how does it work?

Reverse Health is a digital programme for women over 40 that pairs structured fasting windows with nutritional guidance and lifestyle coaching, accounting for hormonal changes during perimenopause and menopause. It does not include prescriber review or pharmacist support as standard.

Reverse Health is a digital health programme designed specifically for women over 40 that incorporates intermittent fasting as one of its core strategies for weight management and metabolic health. The programme combines structured eating windows with nutritional guidance, lifestyle coaching and habit-building tools, tailored to the hormonal and physiological changes that occur during perimenopause and menopause.

Intermittent fasting is not a diet in the traditional sense but rather a pattern of eating that alternates between defined periods of eating and fasting. Common approaches include the 16:8 method (eating within an eight-hour window and fasting for sixteen hours), the 5:2 method (eating normally for five days and significantly restricting calories on two non-consecutive days), and time-restricted eating more broadly.^[9] During the fasting period, the body depletes glycogen stores and begins to draw on fat for energy, a process that may support weight loss and improve insulin sensitivity over time.^[6][7]

Reverse Health positions intermittent fasting within a broader framework that accounts for oestrogen decline, changes in muscle mass and shifts in metabolic rate that are common after 40. The programme typically pairs fasting protocols with higher protein intake and resistance-based activity to help preserve lean muscle, which tends to decrease with age. It is delivered via an app as a lifestyle programme and does not include prescriber review or pharmacist support as standard. Women with existing health conditions, those who are underweight, or anyone who has experienced significant unintentional weight loss should seek advice from their GP or a registered dietitian before starting any structured fasting programme.

Is intermittent fasting safe for women over 40 in the UK?

Intermittent fasting is generally safe for healthy women over 40, but hormonal status, bone health and existing medical conditions should be assessed first. Women on insulin, sulphonylureas or SGLT2 inhibitors must consult their GP before starting.

Intermittent fasting is generally considered safe for most healthy women over 40, but individual circumstances, particularly hormonal status, bone health and any underlying medical conditions, should be assessed before starting. For many women in this age group, perimenopause and menopause bring changes in insulin sensitivity, cortisol regulation and sleep quality, all of which can interact with fasting protocols in ways that differ from younger adults.

Some research suggests that prolonged or very restrictive fasting may increase cortisol levels, which can be counterproductive in women who are already experiencing hormonal fluctuation.^[9] There is also emerging discussion about whether certain fasting windows may affect sleep quality or exacerbate symptoms such as hot flushes, though the evidence in this specific population remains limited and no firm conclusions can be drawn at this stage. Women who are pregnant, breastfeeding or planning a pregnancy should not undertake intermittent fasting without specialist medical advice.

NICE guidance on weight management (NG246) emphasises a person-centred approach and recommends that any dietary intervention be sustainable and nutritionally adequate.^[1][2] Intermittent fasting is not specifically endorsed or discouraged by NICE as a standalone strategy, but it is recognised within broader dietary approaches to energy restriction. Women with a history of disordered eating, those who are underweight (BMI below 18.5), those with type 1 diabetes, adrenal insufficiency, or who take medicines that require food (such as certain blood pressure or diabetes medications) should speak to their GP before starting.

Those on insulin or sulphonylureas face a particular risk of hypoglycaemia during fasting periods and must not adjust their medication without clinical guidance. People taking SGLT2 inhibitors (such as dapagliflozin, empagliflozin or canagliflozin) should be aware that fasting or very low calorie intake can increase the risk of diabetic ketoacidosis, including euglycaemic ketoacidosis, even when blood glucose appears normal. The MHRA has issued safety advice on this risk. Anyone on an SGLT2 inhibitor should discuss fasting with their prescriber before making any changes to their eating pattern.

What does the evidence say about intermittent fasting for weight loss?

Evidence shows intermittent fasting produces modest weight loss but is not meaningfully superior to continuous calorie restriction when total energy intake is matched. The evidence base for women over 40 specifically remains limited.

The evidence for intermittent fasting as a weight loss strategy is broadly positive but consistently shows it is not meaningfully superior to continuous calorie restriction when total energy intake is matched. Cochrane reviews and major randomised controlled trials, including a 2022 trial published in the New England Journal of Medicine comparing time-restricted eating with unrestricted eating in adults with obesity, have found that time-restricted eating produces modest reductions in body weight and waist circumference, with some improvements in fasting glucose and blood pressure. However, when calorie intake is carefully controlled across comparison groups, the advantage of the fasting schedule itself largely disappears, and adherence and individual response vary considerably.^[6][7]

For women over 40 specifically, the evidence base is thinner. Most large trials have not stratified results by menopausal status, making it difficult to draw firm conclusions about this group. Smaller studies suggest that time-restricted eating may help reduce visceral fat, which tends to accumulate after menopause and is associated with increased cardiovascular risk.^[9] Preserving muscle mass during any calorie-restricted approach remains a key concern in this age group, and available evidence supports combining fasting with adequate protein intake and resistance exercise to mitigate muscle loss.

Published trials generally report weight loss in the range of a few percent of starting body weight over twelve to twenty-four weeks, though figures vary widely depending on the protocol, population and degree of calorie restriction achieved.^[6][7] These outcomes are meaningful but modest, and intermittent fasting is unlikely to be sufficient as a sole intervention for significant obesity.

For women whose weight is affecting their health, NICE-recommended interventions include structured behavioural programmes and, where clinically appropriate, pharmacological treatment. Eligibility for weight management medicines in the UK is determined by specific NICE Technology Appraisals and local Integrated Care Board (ICB) commissioning criteria, which vary by medicine and by area.^[11] Your GP or a weight management service can advise on which options you may be eligible for. Intermittent fasting can be a useful component of a broader lifestyle approach but should be considered alongside, rather than instead of, clinically supported pathways where these are available and appropriate.

What side effects should you watch for when starting intermittent fasting?

Common early side effects include hunger, headaches, fatigue and irritability, which typically resolve within one to two weeks. More serious risks include hypoglycaemia, ketoacidosis in those on SGLT2 inhibitors, and worsening of disordered eating patterns.

The most commonly reported side effects when starting intermittent fasting include hunger, headaches, fatigue, difficulty concentrating and irritability, particularly during the first one to two weeks as the body adapts to a new eating pattern. These symptoms are generally mild and tend to resolve as the body adjusts, though they can be disruptive to daily life and work.

Women over 40 should be aware of a few additional considerations. Fasting can sometimes worsen sleep disturbance, which is already common during perimenopause. Eating too little during the eating window, or skipping nutrient-dense foods in favour of convenience, can lead to micronutrient deficiencies over time, particularly in calcium, vitamin D and iron, all of which are important for bone and cardiovascular health in this age group. Dizziness on standing (postural hypotension) can occur, especially if fluid intake is insufficient during the fasting window.

More serious but less common concerns include:

• Hypoglycaemia in women taking insulin, sulphonylureas or other glucose-lowering medicines

• Ketoacidosis in women taking SGLT2 inhibitors, including euglycaemic ketoacidosis where blood glucose may appear near-normal; seek urgent medical attention if you develop nausea, vomiting, abdominal pain, excessive thirst or unusual fatigue while fasting on these medicines

• Worsening of disordered eating patterns, including restriction-binge cycles

• Electrolyte imbalance with very prolonged or very low calorie fasting

• Exacerbation of gallstone symptoms, as reduced bile flow associated with prolonged fasting or rapid weight loss can trigger symptoms in those with existing gallstones^[14]

If you experience chest pain, severe dizziness, fainting, persistent vomiting or signs of hypoglycaemia (shakiness, sweating, confusion), contact your GP or call NHS 111 for urgent advice. Do not attempt to manage these symptoms by adjusting prescribed medication without clinical guidance. Suspected side effects from licensed medicines can be reported via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk.

How do you get started with intermittent fasting safely in the UK?

Start with a GP conversation if you have existing health conditions, take regular medication or have a history of disordered eating. A gradual approach, beginning with a 12-hour overnight fast and extending incrementally, is safer than starting immediately with a 16:8 or 5:2 protocol.

Starting intermittent fasting safely in the UK begins with a conversation with your GP, particularly if you have any existing health conditions, take regular medication or have a history of disordered eating. Your GP can review your current health status, flag any contraindications and, where appropriate, refer you to a dietitian or structured weight management programme through the NHS. Referral routes and eligibility for NHS Tier 2 and Tier 3 weight management services are determined locally by your ICB, so availability and criteria vary by area.

For women who are otherwise healthy and wish to try intermittent fasting independently, a gradual approach is advisable. Beginning with a 12-hour overnight fast and extending it incrementally over several weeks is less disruptive than starting immediately with a 16:8 or 5:2 protocol. Prioritising nutrient-dense foods during the eating window, including adequate protein, vegetables, wholegrains and healthy fats, helps to ensure nutritional adequacy. ESPEN and PROT-AGE consensus guidance suggests that older adults generally benefit from a higher protein intake than younger adults to support muscle maintenance, though the optimal amount varies by individual factors including kidney function; a registered dietitian can advise on what is appropriate for you.^[10]

Hydration is important throughout the fasting period. Water, plain herbal teas and black coffee are generally considered acceptable during fasting windows, though individual programmes may vary in their guidance. Avoiding high-intensity exercise during the initial adaptation phase can reduce the risk of dizziness or fatigue.

For women whose weight is affecting their health and who are looking for a clinically supported approach, a range of options exists. Bolt Pharmacy is a GPhC-registered online pharmacy (GPhC regulates pharmacy premises in Great Britain; pharmacies in Northern Ireland are regulated by the PSNI) offering online weight-management consultations, with prescriber review and pharmacist support, where clinically appropriate options may be considered.^[12][13] Whichever route you choose, look for services that involve a qualified prescriber, take a full medical history and provide ongoing clinical support rather than a one-off assessment.

Scientific References

1. Overweight and obesity management (NG246).
2. Overweight and obesity management (NG246) – General principles of care.
3. Overweight and obesity management (NG246) – Full guideline PDF.
4. SGLT2 inhibitors: updated advice on the risk of diabetic ketoacidosis.
5. Forxiga 10 mg film-coated tablets – Summary of Product Characteristics.
6. Calorie Restriction with or without Time-Restricted Eating in Type 2 Diabetes (Liu D et al.).
7. Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters (Lowe DA et al.).
8. Effectiveness of Early Time-Restricted Eating for Weight Loss (Jamshed H et al.).
9. Intermittent fasting and health outcomes: an umbrella review (Sun ML et al.).
10. Protein intake and exercise for optimal muscle function with aging: recommendations from the ESPEN Expert Group (Deutz NEP et al.).
11. A guide for prescribing medicines to manage overweight and obesity (TA1026).
12. General Pharmaceutical Council – About GPhC (regulates pharmacy premises in Great Britain).
13. Pharmaceutical Society of Northern Ireland – About PSNI (regulates pharmacies in Northern Ireland).
14. Gallstones.

Frequently Asked Questions