Why Some Like It Hot: Food, Genes and Cultural Diversity

  • Gary Paul Nabhan
Island Press: 2004. 223 pp. $24 0195165829 | ISBN: 0-195-16582-9
Credit: ILLUSTRATIONS BY CHRISTIAN DARKIN

It's not that we are what we eat, proposes Gary Nabhan, but rather, we are what foods our ancestors ate and what genes they gave to us. In Why Some Like it Hot, Nabhan argues that natural selection and other evolutionary processes mediated by food choices unique to each geoclimatic and cultural domain have played important roles in generating human genetic diversity.

According to Nabhan, the time period for this evolution is likely to have been much shorter than is generally supposed. Our unique gene profiles evolved within the past few thousand years or so, perhaps as mutations caused by secondary compounds in staple foods and culinary herbs that were indigenous to certain geoclimatic regions. These genomic profiles could have been moulded by food choices, and by pressure from endemic diseases, to reduce the risk of disease.

This view departs from the darwinian idea that our current gene pool resulted from a very slow process of random selection to maximize individuals' survival. The fact that 99.9% of our genome is shared by all humans, present and past, is cited as evidence of an exceptional genetic stability that arose many millennia ago, perhaps during and before Palaeolithic times.

This observation of early genetic similarity and stability has suggested to some observers that there is a one-size-fits-all diet, perhaps one that was commonly used during Palaeolithic times, but Nabhan challenges this view. He points out, as others have, that of the 3 billion nucleotides in the human genome, 3 million of them (0.1%) have remained in play and can be used to create genetic diversity. A change of only one nucleotide can make a substantial difference.

Nabhan identifies a group of 26 ‘disease genes’ that are likely to have been fashioned by food factors and endemic diseases. He cites adult-onset diabetes, lactose intolerance and heritable food allergies as examples of interactions between genes, food and disease. He goes on to say that a large number of us are subject to one or more of these genetic ‘disorders’, as some would call them — indeed they are so common that they should be considered normal.

He discusses in considerable depth the extensively studied link between malaria, sickle-cell anaemia, the consumption of fava beans, and glucose 6-phosphate dehydrogenase (G6PD) deficiency, in order to illustrate how a careful study of biology, culture and history can be much more rewarding than one of these disciplines alone. He takes the reader on a trail of discovery, visiting the Mediterranean island of Sardinia, where malaria has long been endemic. Here the traditional springtime consumption of fava beans offers those with the genetic disorder of G6PD deficiency some protection against the mosquito-borne disease. Coupling cultural, biological and historical analyses in this way is the basis for the field of nutritional ecogenetics.

Nabhan also cites examples that tend to be found in regions of the world, particularly islands, where the resulting interactions became reasonably well established and remained stable. For example, on the island of Crete and elsewhere in the Mediterranean region, a high-fat diet is associated with a lower risk of heart disease than would be expected from studies of other Western subjects. His travels to these regions and his discoveries are presented as engaging personal experiences. He ends his book with a particularly notable example of the remarkable clinical experiences of Terry Shintani and colleagues, who have studied the food sensitivities now suffered by indigenous Hawaiians as they adopt a modern Western diet.

The story told by Nabhan is thought-provoking. He implies that each of us, as individuals, should consider our food choices and their health effects with reference to our own evolutionary past. However reasonable this argument seems, it leaves unanswered the critical question of how such information can be used to create contemporary dietary advice for the public. Most people now are a heterogeneous mixture of genes and food habits that will be virtually impossible to untangle in a way that can tell us what we should be eating to be healthy. Even if we knew the evolutionary pedigree of our contemporary genes — which is most improbable — we would be hard put to match our genetic predispositions with the specific foods likely to make us most healthy. I dread to think what the marketplace will make of this account.

In decrying the one-size-fits-all diet proposal promoted by some dietary advocates, Nabhan seems to ignore the remarkable nutritional range and food choices that exist within such supposedly monolithic diets. For example, the recommended low-fat, whole-food, plant-based diet neither connotes an unvarying diet nor implies exactly the same health benefits for all consumers. It allows for, and even encourages, the consumption of a wide variety of such foods. But the diversity for different regions and different groups of people can still be used to generate most of the same health benefits. This is the beauty of the work of Shintani and his colleagues, who have produced remarkable health benefits when obese and diabetic native Hawaiians are re-introduced to their native whole-plant-based foods, which are low in fat and high in fibre and antioxidants. In a similar way, a range of different plant-based foods can be used to control or even reverse a variety of serious diseases.

It is remarkable that meaningful genetic adaptation can occur in a few thousand years or so, but even more so that genetic-like adaptations can occur within only one or two lifetimes. Dietary experiences before or shortly after birth, either direct or maternal, can imprint substantial biochemical and morphological changes that become stabilized well into adulthood as if they were genetic — yet they are more likely to be post-transcriptional or post-translational. Such is the nature of dietary adaptation, a process that is continually at work, short term and long term, minimizing harm and making the most of what food and other resources are available.

Despite these minor criticisms, the book is well worth reading, for it should stimulate an important debate about what constitutes dietary adaptations and sensitivities.