Food and diet

Big breakfast 'boosts fertility' for some women

“Eating a hearty breakfast could help women with fertility problems,” The Daily Telegraph reports. Researchers have found that eating a hearty meal in the morning, rather than the evening, may help combat the effects of 
polycystic ovary syndrome (PCOS) – a major cause of infertility.

The underlying cause of PCOS is unknown, but the condition is associated with hormonal imbalances leading to missed or absent periods, which, in turn, can make it hard for the women to conceive.

Many women with PCOS are also found to have abnormal insulin levels, or are “insulin resistant”, which means they don’t respond to insulin normally. This then leads to higher than normal levels of testosterone in the blood, which disrupts the menstrual cycle.

Reducing insulin with weight loss or medication may improve fertility, however these are not good options for slim women. So the researchers wanted to see if the timing of meals led to a better control of insulin in women with PCOS.

Researchers asked 60 slim women with PCOS to eat 1,800 calories each day for 12 weeks. One group of women was asked to eat most of their calories at breakfast, the other group was asked to eat most at dinner. By the end of the study, half of the women in the breakfast group had ovulated at least once, compared to a fifth of the "dinner group", which suggests improved fertility.

Although these results are encouraging, the study was only small and, despite the blood results suggesting improved fertility in the "big breakfast" group, we don’t know whether this actually resulted in improved chances of the women becoming pregnant.

Where did the story come from?

The study was carried out by researchers from the Sackler Faculty of Medicine at Tel Aviv University and the Institute of Biochemistry, Food Science and Nutrition at The Hebrew University of Jerusalem. They report that no funding was received.

The study was published in the peer-reviewed medical journal, Clinical Science.

The study was generally well reported in the UK media.

What kind of research was this?

This was a randomised open-label trial that aimed to see if a high-calorie breakfast could reduce the amount of insulin that is released per day in slim women with polycystic ovary syndrome (PCOS).

While there were two different groups in this trial, there was no control group of women eating their normal diet. This means that any differences seen could be due to the change in diet – eating 1,800 calories per day (which is slightly under the recommended limit for women of 2,000 calories), rather than the timing of the meals.

To better examine the effect of diet upon fertility, a randomised controlled trial including a control group continuing with their normal diet, including more people, and that examined effect on longer-term pregnancy outcomes would be required.

What did the research involve?

The researchers recruited 60 women with PCOS aged between 25 and 39 who were a healthy weight (body mass index (BMI) of less than 23.9kg/m2). Women were excluded from the study if they had:

  • taken any medication known to affect glucose, insulin or reproductive hormones in the previous six months
  • diabetes
  • change in body weight of more than 4.5kg in the previous six months or on a diet
  • change in physical activity in the previous six months

The women were randomly spilt into two groups, the first advised to eat a high-calorie breakfast, the second group a high-calorie dinner. Each group was given advice about eating a normal diet of 1,800kcal per day for 12 weeks, which should not have resulted in any change in weight. They were also asked to have no more than two alcoholic drinks per week during the study.

The high-calorie breakfast plan group was advised to have:

  • a large meal at breakfast of 980kcal
  • a medium-sized meal at lunch of 640kcal
  • a small meal at dinner o 190kcal

The high-calorie dinner plan group were advised to have:

  • a small meal at breakfast of 190kcal
  • a medium-sized meal at lunch of 640kcal
  • a large meal at dinner of 980kcal

The women wrote a detailed diet record for three days at the beginning of the study and every two weeks.

At the beginning of the study, the researchers measured:

  • progesterone levels during the follicular phase of the menstrual cycle (the first half of the cycle, where the ovarian follicles mature prior to the release of an egg at ovulation) – progesterone is a hormone associated with the female reproductive system
  • insulin
  • glucose
  • steroid hormones
  • sex hormone-binding globulin (SHBG) – a hormone with a similar function to progesterone

The researchers then measured the women’s progesterone levels every week. If the progesterone levels increased to more than 2ng/ml and menstrual bleeding occurred within two weeks, then they recorded that the woman had ovulated (released an egg). All of the initial tests were repeated at the end of the study.

The researchers also measured body mass, blood pressure and waist circumference every two weeks.

What were the basic results?

Twenty-five women on the high-calorie breakfast plan completed the study as did 26 women on the high-calorie dinner plan.

There were no statistically significant differences between the groups in terms of age, BMI, waist:hip ratio or body fat at the beginning of the study and this did not change after 12 weeks.

Blood tests results were the same in each group at the beginning of the study. However, after 90 days the fasting blood glucose concentrations of the high-calorie breakfast group significantly decreased by 8% (from 89.1 to 81.8 mg/dl) and insulin levels decreased by 53% (from 14.3 to 6.7 microIU/ml). There was no significant change in fasting glucose or insulin in the high-calorie dinner group.

Hormone levels did not change in the high-calorie dinner  group, but in the high-calorie breakfast group the SHBG level doubled and the level of testosterone halved.

No women ovulated in the first month of the study, but by the end of the study, 50% of the women in the high-calorie breakfast  group had ovulated at least once, compared to 20% of the high-calorie dinner group. Five women in the high-calorie breakfast  group ovulated twice, but none did in the high-calorie dinner group.

How did the researchers interpret the results?

The researchers concluded that eating a high-calorie breakfast and low-calorie dinner can reduce insulin resistance and lower the levels of a certain enzyme known to be more active in women with PCOS. This can reduce the high levels of testosterone and improve ovulation rate for slim women with PCOS.


This study has shown that in slim women with PCOS, eating most of the daily calories at breakfast can reduce levels of insulin by 8% and testosterone by 50% with no weight change. In this study, this led to half of the women in the breakfast group ovulating at least once, compared to a fifth of the "dinner group", which suggests improved fertility.

Although these results are encouraging, there are some limitations to the study, including:

  • Ovulation was only recorded over a three-month timespan, and it is not clear how often any of the women were ovulating in the previous year.
  • This study was reliant on the accuracy of the women to recall and record their diet for three days every two weeks. In addition, these three days may have been misrepresentative of the diet as a whole as the study does not provide details of which days of the week the diet diaries were kept – and they may differ substantially at the weekends.
  • This was a small study and did not include a control group of women continuing with their normal diet. Without a control, the fact that all women changed to an 1,800 calorie per day diet may mean that there were other influences on the hormone levels in both groups resulting from the change in diet, rather than just the timing of meals alone.
  • Though the hormone levels suggest improved fertility, we don’t know whether this actually resulted in improved chances when trying to become pregnant – no women became pregnant during the course of the study

While these results are encouraging, it is important to remember that one of the main ways to improve fertility in PCOS is to have a healthy weight with a BMI between19 and 25kg/m2. If you are overweight, losing just 5% of your bodyweight can lead to significant improvement in PCOS symptoms.

Eating a big breakfast without substantially reducing the evening meal may be counterproductive as it is likely to lead to weight gain. This study has also not examined the health effects of continuing with the big breakfast, small dinner calorie diet in the longer term beyond three months.

If you are affected by PCOS and are having problems conceiving there are medications that may help, and your GP or consultant should be able to advise you about them.

NHS Attribution