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Polycystic Ovary Syndrome dietary options and their role in preventing type 2 diabetes

Polycystic Ovary Syndrome dietary options and their role in preventing type 2 diabetes

This article examines the different weight loss options for a patient who is at high risk of diabetes and suffers from Polycystic Ovary Syndrome.

Case study – patient A

A 36-year-old comes to see you with HbAc1 46.4mmol/mol (6.4%). FHx diabetes.

She also has Polycystic Ovary Syndrome (PCOS), diagnosed at the age of 16. Her height is 5.2ft, weight 60kg and waist circumference 102cm.

The patient attends the clinic due to being called in to discuss her HbAc1 result following her being identified as potentially high risk for diabetes, and to seek advice for diabetes prevention. As per current NICE (2017) guidelines HbA1c between 42.1mmol/mol – 46.4mmol/mol (6-6.4%) represents a high risk of diabetes.

The patient is advised that the key thing in reducing her risk of progressing to full blown diabetes is to lose weight with a balanced diet and exercise.

She declines a referral to a diabetes prevention programme, which is recommended as per NICE (2017) guidelines. However, whilst leaving, she asks about the following diets: very low-calorie diet, intermittent fasting and low glycaemic diet.

The benefits of weight loss in women with PCOS is well documented; however, the optimal diet composition is less known. Targeting 5-10% weight loss is known to improve menstrual function. Hence, this may be a sensible target for patient A. 

Very-low calorie diet (VLCD)   A very low-calorie diet is a restricted diet limited to 800 calories a day or less. It often consists of three meal replacement products a day (e.g. shakes, bars or soups) and an allowance of non-starchy vegetables. These diets are not nutritionally complete and should normally be followed for a maximum of 12 weeks under medical supervision. These diets have historically been met with scepticism, as the evidence base has relied on short studies with varying long-term outcomes.1 However, more recently larger studies highlighted promising long-term outcomes. Specifically, there is a notable reduction in central body fat and almost half of those who complete the diet maintain >10% weight loss at 12 months.2 The VLCD has even shown a sustained improvement in metabolic control, causing remission of type 2 diabetes by 24 months in over a third of those who completed the VLCD for 8-12 weeks. This was demonstrated in the DiRECT open-label, cluster- randomised trial.3 This was where 46% were in remission and 24% had at least 15kg of weight loss. A notable difference however between the earlier and more recent studies is the more intensive follow up offered during the weight loss and food reintroduction phase. Follow up with a specialist was offered every 2 weeks, which although critical in avoiding dietary lapses, may not be achievable in current practice. However, there is evidence of VLCD in diabetes prevention in the PREVIEW study with both weight loss and reduction in HbAc1%.    
Intermittent Fasting (IF)   Intermittent fasting has been practiced for religious and health reasons for hundreds of years. The definition of an intermittent fasting diet varies, but it always involves periods of time where you are taking in very little food, at regular intervals.4
• The 16:8 diet involves fasting for 16 hours per day and eating within an eight-hour window. This is usually done by only eating from midday till 8pm.
• The 5:2 diet involves eating only 25% of a normal calorie intake on two non-consecutive days per week.
• A 24 hours fast involves consuming no calories on one day of the week or month.   In the last 10 years IF has gained a lot of attention. Observational studies have hinted towards a lesser prevelance of diabetes in individuals who periodically fast, irrespective of body weight.5 Animal studies have shown IF to reduce circulating levels of glucose, insulin and the hunger hormone leptin, but human studies have not conclusively shown the same.6 Currently the evidence for IF is limited and often does not show superiority compared to conventional calorie-controlled diets.7     
Low GI diet   National guidance for the nutritional management of PCOS reads ambiguously.  Weight loss is frequently recommended for women with PCOS who are overweight or obese, however there is no evidence of any one diet type being superior over another.8, 9, 10  The BDA (British Dietetic Association) supports the use of a low GI diet for ladies with PCOS.11   Glycaemic index (GI) is a rating which denotes how quickly a carbohydrate food cause your blood glucose levels to rise after it has been eaten.11 Low GI diets have been shown to attenuate post-prandial insulin release which in theory can be beneficial to women with PCOS as the syndrome can cause post-prandial hyperinsulinaemia12.   The weight loss and glycaemic improvements seen from a low GI diet for people with type 2 diabetes is well documented and is a recommended diet therapy in NICE guidance.13 Weight loss improves hormone and metabolic markers in women with PCOS, but interestingly a high protein/low GI diet appears to significantly improve insulin sensitivity and decrease inflammatory markers.14, 15 Lower carbohydrate diets have also been shown to increase energy expenditure, particularly in those who are insulin resistant, like in PCOS.16  

The key factor to consider here for this patient is PCOS. PCOS is a common endocrine disorder amongst women of reproductive ages. As well as fertility issues, PCOS is known to cause other metabolic disorders including insulin resistance, dyslipidemia and hyperinsulinemia and these in turn can lead to hyperandrogenism which can affect fertility.17 Thirty per cent of ladies with PCOS will develop type 2 diabetes.

Therefore, in patient A’s case, a diet therapy that improves body weight, insulin sensitivity and reduces circulating insulin levels should be considered as part of a holistic treatment plan. Problems associated with long term adherence to continuous energy restriction for weight management are well known, therefore this should also be explored with patient A when finalising her care plan.18

The difficulty in losing weight is often blamed on the PCOS, in particular the link between hyperinsulinaemia and weight gain.19 There is clear evidence that a reduction of 5-10% of body weight reduces the risk of preventable diseases such as diabetes,20 and is known to improve menstrual function, and may be a sensible target for this lady.8 It is also imperative to consider the impact of lifestyle and environmental factors such as commuting, work environment and stress levels because these factors can influence one’s health outcome.

Problems of long-term adherence to continuous energy restriction for weight management are well known.18 Therefore, when discussing the suitability of any diet that requires restrictions, factors such as daily activity levels should be taken into account. Primarily, a diet approach should focus on improving insulin resistance / improving insulin sensitivity.

Stress hormones prevent fat loss / gain weight gain – with PCOS any additional stress such as being told there she is a high risk of type 2 diabetes can cause a further imbalance.21 Hence, the diet advocated to the patient should be a diet which causes least stress possible. The advice should also include the importance of maintaining a good sleep pattern, since the lack of sleep will increase the stress hormones such as cortisol and it will prevent weight loss but also making the patient more insulin resistant.22

Reduced fibre intake in patients’ diet can contribute to symptoms of PCOS , gut disturbances and prevent body fat percentage loss.23

Educating PCOS patients in the importance of exercise regime is vital in making sure the objective of weight loss is achieved with the reduction of body fat percentage and not the loss of muscle mass or bone density24.

The calorie restricting diet can also prevent the patient from getting in good fats in the diet ,which are required to keep the female hormones in balance.6

The inability of healthcare professionals to show a good understanding of the problems faced by PCOS patients can inhibit a good patient relationship and negatively affect health outcomes of patients.25


There is growing evidence base for the short-term use of restrictive diets (like VLCD and IF), followed by achievable calorie-controlled diets for weight maintenance. However, the aim should be long-term maintenance of healthy weight.

Diets which are restricting can cause nutrient deficiencies and hormonal imbalance in PCOS patients which can negatively affect fertility. The patient’s psychological wellbeing should be considered when formulating a treatment plan. Hence, the clinician should focus of the patients nutritional and exercise requirements which would result is weight loss.

The above diets are not practical and sustainable for long term management of PCOS. Clinicians should be advocating lifestyle and environmental modification to prevent diabetes and management of PCOS.


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  3. Lean, M., Leslie, W., Barnes, A., Brosnahan, N., Thom, G., McCombie, L., Peters, C., Zhyzhneuskaya, S., Al-Mrabeh, A., Hollingsworth, K., Rodrigues, A., Rehackova, L., Adamson, A., Sniehotta, F., Mathers, J., Ross, H., McIlvenna, Y., Welsh, P., Kean, S., Ford, I., McConnachie, A., Messow, C., Sattar, N. and Taylor, R. (2019). Durability of a primary care-led weight-management intervention for remission of type 2 diabetes: 2-year results of the DiRECT open-label, cluster-randomised trial. The Lancet Diabetes & Endocrinology, 7(5), pp.344-355.
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