The science

A lot of us fall into the trap of thinking all carbs are bad, and the first port of call when dieting is to cut out all carbs. But this misses an important nuance – the difference between easily digested carbs and slowly digested carbs. This week we explain how this important difference can impact ovulation and fertility.

Easily digested carbs include:

  • White bread, pasta, rice  
  • Potatoes
  • Sugared sodas
  • Cakes, doughnuts and pastries
  • Pizza
  • Potato crisps, corn crisps, chips
  • Beer

Slowly digested carbs include:

  • Wholegrains:
    • Wholegrain bread, pasta, rice
    • Oats
    • Popcorn
    • Barley
    • Whole or cracked wheat
  • Beans
  • Vegetables (including the skin)
  • Whole fruits (including the skin)


Research shows that carbs can influence fertility. Eating lots of easily digestible carbs increases the odds that you’ll find yourself struggling with ovulatory infertility. Choosing slowly digested carbs that are rich in fibre can improve fertility. Research also shows that a diet rich in slow carbs and fibre before pregnancy helps prevent gestational diabetes.

So why are some carbs slower to digest? Wholegrains are foods that contain all three parts of a grain’s bounty: its fibrous bran, starchy endosperm, and vitamin rich germ. So it takes a while for your stomach acid and digestive enzymes to break through the bran. Once they do, they are able to attack the starch and turn it into sugar.

And how are easily digestible carbs different? Processing completely changes the character and the content of the grains. Milling strips away the bran and germ, making the grain easier to chew, easier to digest, and easier to keep with refrigeration. Refining wheat creates fluffy flour that makes light, airy breads and pastries. But removing the bran and germ strips away more than half of wheat’s B vitamins and 70% of its iron (both of which are important for ovulation and conception!) along with 90% of vitamin E and virtually all of the fibre. Highly processed carbs therefore give you a quick blast of blood sugar and only a shadow of the grains original nutrients.

Why are easily digestible carbs bad for our health? All of our cells constantly need energy. That’s why insulin and glucagon work together to keep blood sugar fairly steady, even in between meals. But eat a meal full of easily digestible carbs means your blood sugar skyrockets. This means your body responds with a big injection of insulin. Problems arise when our bodies get used to having high levels of insulin, and have trouble using what used to be a normal amount. This  is known as insulin resistance, and is the first step towards type 2 diabetes.

And for our fertility? Carbs are important because more than any other nutrient they determine your blood sugar and insulin levels. When these levels rise too high they disrupt the balance of hormones needed for reproduction, and these hormonal changes can impact ovulation.

In fact, women who had a high glycemic load (the higher the glycemic load, the more easily digestible carbs in the diet) were 92% more likely to have ovulatory infertility than women in the lowest category (after accounting for age, smoking and other factors that impact fertility)

Overall, research shows that it’s not the amount of carbs in our diet that is important, but the quality that is important for fertility. Eating slowly digested carbohydrates can improve ovulation and your chances of getting pregnant.


Your change for the week

Swap your carbs! Swap from white to wholegrain, and from easily digestible to slowly digestible. Here are some ideas:

  • Have porridge, wholegrain cereal (with no added sugar) and wholegrain toast for breakfast
  • Swap fizzy drinks and fruit juice for water
  • Don’t ditch pasta, but choose wholegrain varieties
  • Bank on beans: beans generally have a small effect on blood sugar and insulin
  • Eat plenty of vegetables and whole fruit (not juice)
  • Eat great grains: including quinoa, pearled barley, millet, rye berries, spelt berries, wheat berries
  • Feeling peckish? Swap chocolate for fruit/nuts and crisps for popcorn

These changes will help you have a low GI diet, which is also recommended for women with PCOS – as women with PCOS are known to have higher than normal insulin levels.


Recipe inspiration

Rye toast with avocado and tomatoes

  • ½ slices of rye bread (toasted)
  • Smash ½ an avocado with a squeeze of lemon juice
  • Quarter some cherry tomatoes

Whole-wheat start

  • Two Weetabix (or supermarket own variety)
  • Semi-skimmed milk
  • A sliced banana and a handful of blueberries

Veggie chilli

(This recipe delivers a good dose of iron and folate (the beans), and that iron is more easily absorbed because of the vitamin C from the bell peppers and tomatoes)

  • 1 red onion
  • 1 dried smoked chipotle or ancho chilli
  • ½ a fresh red chilli
  • 1 teaspoon sweet smoked paprika
  • ½ teaspoon cumin seeds
  • 1-2 cloves of garlic
  • 1 big bunch of fresh coriander
  • olive oil
  • 2 mixed-colour peppers
  • 1 x 400 g tin of red kidney beans  
  • 1 x 400 g tin of black beans
  • 700 g passata

Peel and halve the red onion. Put the chillies, onion, paprika and cumin seeds into the processor, squash in the unpeeled garlic through a garlic crusher, then add the coriander stalks (reserving the leaves) and 2 tablespoons of oil, and whiz until fine.

Tip into the pan. Deseed and roughly chop the peppers, drain the kidney beans and black beans, then add to the pan with a pinch of sea salt and black pepper and the passata, stir well and put the lid on.