Scientists uncover why women crave chocolate and crisps at certain times of the month – and confirm ‘it’s not made up’

• The brain reacts less to insulin in the pre-menstrual phase of a woman’s cycle 
• This could also help to explain premenstrual mood swings, experts say 

Women who feel ravenous and crave chocolate and crisps every month really do have good reason.

A study has found a change in women’s brains at a certain time of the month which could affect their appetite and desire for junk food.

Researchers discovered that in the pre-menstrual phase of a woman’s cycle, after ovulation but before her period arrives, a brain region called the hypothalamus reacts less to the hormone insulin.

Most people know about insulin, which is produced by the pancreas, in relation to diabetes because it regulates blood sugar.

But when insulin reaches the brain, previous evidence suggests it can make women less hungry and prone to snacking.

The brain reacts less to insulin in the pre-menstrual phase of a woman’s cycle, which could make women crave chocolate and crisps at certain ties of the month

Therefore, the new finding that insulin doesn’t work as well in the brain when women are pre-menstrual, could help to explain their increased appetite and unhealthy cravings at this time.

The findings come from scanning the brains of 15 women in an MRI machine.

Senior author Professor Martin Heni, who conducted at the study the University of Tuebingen in Germany, said: ‘There is not as much research about insulin in the brain as there is in the body.

‘This is the first evidence that it has less effect on women at a certain point in their menstrual cycle.

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‘The implication that this could help to explain hunger and cravings in pre-menstrual women is really helpful – it shows that women who struggle with this are not making it up.

‘However our study did not directly look at these effects in women.’

The study, published in the journal Nature Metabolism, gave the 15 women a nasal spray of insulin to mimic what happens when the hormone crosses into the brain.

This caused significant activity in a brain region called the hypothalamus during the ‘follicular’ phase of their cycle – from the day after their last period until ovulation.

But there was less brain activity in the ‘luteal’ phase, when women are pre-menstrual – after ovulation but before their period.

This could also help to explain premenstrual mood swings, as insulin action in the brain may affect emotions.

Researchers suspect that insulin is needed by women in the first half of their cycle, as the hormone controls glucose in the body, so can recruit energy to help them produce an egg and thicken the lining of their womb in case they become pregnant that month.

But this process is less necessary after ovulation.

The lack of sensitivity to insulin seen in the brains of pre-menstrual women is, however, separate to the lack of sensitivity to insulin seen the rest of the body which can lead to type 2 diabetes.

It means women should not fear a major surge in their blood sugar in the second half of their menstrual cycle.

However the temporary lack of sensitivity to insulin in the brain could, over decades, contribute to more fat being stored within the body.

It means women’s pre-menstrual brain changes could be one of the reasons for why they generally have more body fat than men.

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