The Fertile 40s Diet

Want to bolster your fertility or prolong your reproductive window into your forties? Well, according to Australian fertility expert, Dr David Knight, you first need to sit down to a meal of fermented vegetables and soy that he describes as smelling of decaying flesh. Dr Knight has spent over two decades studying the link between nutrition and fertility, and has devised the much talked about Fertile 40s Diet. And the good news is, you don’t need to embrace sauerkraut – you can jump straight to some of the yummiest ingredients nature has to offer.

“One of the biggest problems with fertility that we see in developed countries is polycystic ovary syndrome,” Dr Knight explains. “Around 1/3 to ½ of women who experience problems conceiving have polycystic ovary syndrome.

“Of course genetics play a role, but without question this condition is worsened by diet.

“And this can absolutely be turned around.”

The key, says Dr Knight, is to up your intake of polyamines. “Polyamines are essential for the maturation of eggs and sperm,” he explains.

Polyamines are naturally present in the human body and can be topped up by the consumption of foods high in the enzyme that creates them, Dr Knight explains. Aging and a diet low in this enzyme can see a decrease in polyamines and a decrease in fertility.

In his research, Dr Knight has identified three types of polyamines that play a role in fertility: Putrescine, Spermidine, and Spermine, and these form the basis of the Fertile 40s Diet.

The Fertile 40s Diet

“In general, as the polyamines putrescine, spermidine and spermine are essential for cell renewal, they are also needed to keep the body healthy,” says Dr Knight. “Having a fertile body requires having a healthy and balanced diet, and increasing the intake of polyamines may assist with your overall fertility if you are trying to conceive.”

The best way to bolster your polyamines level is to increase your intake of these key ingredients.

  • Putrescine:  found in aged cheeses, potatoes, canned/frozen vegetables, oranges and frozen prawns.
  • Spermidine: found in mature cheeses, soybeans, fermented tea, mushrooms, potatoes and fresh bread.
  • Spermine: found in cereals, canned or frozen vegetables, meat products, particularly red meat and poultry.

If completely overhauling your diet is not really on the cards, you just need to know that foods with the highest measured polyamine levels include fresh grapefruit juice, orange juice and oranges.

Dr Knight recommends an average daily polyamine consumption of about 3.5-5mg per day.

While diet alone will not guarantee fertility into your forties, Dr Knight says that everything you do makes a difference. “When it comes to fertility there is no such thing as bad luck,” Dr Knight explains. “There are just choices.”

Dr David Knight heads up a team of IVF specialists at the award winning Demeter Fertility. Visit them at

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