One of the least palatable facts about human biology lies in the womb. Chalk it up to Freud, but sometimes it helps to see the foetus as a giant cuddly parasite. Not only does it absorb the lion's share of the host's nutrients during gestation, it actually has the ability to modify her appetite in its favor. That's partly why expecting mothers develop all sorts of undesirable cravings. So should you welcome your new overlord and eat as it pleases?

A mother's gastronomical instincts used to give excellent dietary advice, but things have changed in the last hundred years or so, especially when it comes to food. Our genes know nothing about artificial flavorings, aerosol cheese, or even margarine.

Actually, the story of margarine says it all. The hydrogenated, solidified vegetable oil now enjoys a questionable reputation as the double-crossed agent of health foods. Only in recent years have we come to a firmer understanding of lipids, an absurdly jejune class of fats known since the advent of chemistry.

Depending on a one-syllable prefix or suffix, fats are either essential to your health, toxic in the long run, or as with omega-6, both – which proves that life is a fatal disease. Omega-6 is a less-known relative of omega-3, a commonplace macronutrient formerly of cardiovascular disease. They are both a form of essential fatty acids as our bodies can not synthesize them from scratch. But omega-6 is beneficial only when accompanied by sufficient omega-3 with which to interact. Left to its own device, it gets bored and wrecks havoc instead.

You can guess how this ends. The vast majority of pregnant women – 85% according to a recent survey – take in too little omega-3 in their diets. Meanwhile, a similar percentage of the general population are chronically overdosed on omega-6, from such innocuous dishes as poultry, eggs, and most vegetable oils. So much for veganism.

But the list of potential risks of omega-3 deficiency does not end with premature death from cardiac failure. One of its principal constituents, DHA, is now associated with nascent neural development. And as any delicatessen knows, brains are chiefly made up of fat, and DHA forms a large part of baby brains.

We are not suggesting any esoteric cuisines here. In fact, were it not for the humongous mercurial scare, we would have cribbed a few fish recipes here and left it at that. Deep-sea fish are abundant in omega-3 and particularly DHA, since they feed on a species of algae that manufactures much of the compound through our food chain. Unfortunately, this concentrating mechanism also works for heavy metal toxins.

At the moment, there is only one trustworthy source of DHA supplements, and that is fish oils which have undergone molecular distillation. Even the hungriest pregnant women would not dream of gorging on these tasteless, unsatisfying pellets. But the next time you're thinking of eating for two, give these a go. In the long run, both your baby and your body would thank you for it.

Insatiable: How Do You Fatten Up an Unborn Baby? by Mike M Gibson