Excerpt from The Genetics of Health,by Sharad P. Paul, M.D.

Patients often ask me about food allergies or what they can (or cannot) eat to improve their skin. The reason our guts matter is because our digestive systems not only provide us with fuel to function, but they also shape our internal cellular environments. We’ve already discussed how the environment and genes are entwined. This may be even more pertinent when it comes to the digestive system because ancient foods may have left genetic footprints, but modern foods are often made with synthetic chemicals that may have repercussions on our wellness.

As you know by now, I am not into rigid diets—because with any regimen comes compulsion, compunction, and guilt. Having said that, humanity is physically at its heaviest in history, and with this corpulence come questions like these:

Is saturated fat bad?
How much sugar can I have?
Baked or fried potatoes?

Britain has just introduced a sugar tax. Historically, there have been salt taxes and prohibition on alcohol—while raising prices by increasing taxes on certain things can bring down consumption, the problem is that laws seek to bind, not educate. All such regulations end up doing is increasing a kind of food trafficking, whereby industries simply try to get around legislations. Food is our sustenance—it shouldn’t be a platform for politics or industry; it should be a platform our bodies function well on. So let’s get rid of hunger, remove guilt, get educated instead, and eat healthy.

The old adage about the way to a man’s heart being through the stomach makes food a currency of love—and for humans, a recent religion. The Italians practice it with great gusto, and the French excel in culinary catechism. But certain foods do make us happy, and others may cause illness in certain people due to genetic variations in our gut metabolisms—especially when diets are not balanced. When it comes to food etiquette, genes work on the concept of good and bad, rather than polite and rude. In this chapter, we will discuss different food types and their genetic implications.

The Three S’s: Salt, Sugar, and Starch

In Revolution, Jennifer Donnelly writes: “The more obscure our tastes, the greater the proof of our genius.” There’s a word for the savory taste found in foods like coffee, Parmesan cheese, Marmite, mushrooms, and cured meats: umami. It’s thought to be in foods due to glutamate, an amino acid needed for brain function. Monosodium glutamate (MSG), the chemical found in many processed foods, naturally has this taste, as does human breast milk. From an evolutionary perspective, umami taste receptors evolved for us to sense glutamate to help our brains, while bitter taste receptors evolved to detect poisons.

I begin with salt only because salt is connected to the origins of life, in the depths of the seawater. Is life possible without salt? Possibly not; in differing doses, salt has historically been a medicine to help wounds heal and to induce vomiting. Of course, it has had wide use as a preservative. Learning our origins, saline and otherwise, and understanding the origins of our species’ sustenance is important. Ultimately, we have to do this for ourselves—we owe it to our bodies.


Before the age of hunting tools, people simply ate fruits and vegetables or tried to grab small insects. Even when meat began to be eaten and made up the majority of the diet, humans’ salt intake was still most likely less than 1500 milligrams per day. In fact, even today, the Yanomani Indians in Brazil, who inhabit rainforests and still retain ancient dietary patterns, consume less than 500 milligrams of sodium per day. In contrast, a single can of tomato soup can contain 880 milligrams of salt.

While primitive, tool-less hominids ate very little salt, salt attained great importance with the advent of hunting, as people realized its value as a preservative. Saltiness would have, in the early stages, been an acquired taste until genes began doing their thing. But this is not the only reason salt is heavily used in processed food and artificial flavorings now. Salt in higher concentration suppresses bitter taste, which means that adding salt makes processed food less bitter and, therefore, tastier. As the chemicals in our processed foods are bitter when consumed on their own, salt is added, often in alarmingly high quantities. A high salt intake has clearly been shown to increase heart disease and deaths from heart disease and strokes. In spite of the medical evidence, industry lobby groups like the Salt Institute resist restrictions on salt concentrations, suggesting that there is no statistical evidence.

An experiment on chimpanzees showed that those that were raised on a high salt diet developed high blood pressure, whereas their siblings on a normal diet did not. We know that salt is irrevocably linked to kidney function—kidneys either retain or excrete salt based on the direction given by certain hormones. Further proof of the link between high salt intake and kidney disease is confirmed by the fact that any inherited diseases that end up causing kidney problems tend to increase salt absorption by the kidneys. Meta-analyses have shown that reducing salt does lower blood pressure. Interestingly, even though preference for the taste of salt is not present at birth, infants between four and twenty-three months old begin to show a preference for moderately salty solutions over water, and increased salt diets in infants can also cause higher blood pressure by age seven!

Professor Graham MacGregor from the Wolfson Institute of Preventive Medicine and honorary consultant physician at Saint George’s Hospital, London gave a lecture titled “Salt: Neptune’s Poisoned Chalice” in which he stated, “Mammals are designed to live away from the sea and not eat salt.” Marine mammals that feed on fish consume food with a salt content similar to that of their own blood, thereby avoiding fluid retention or leakage. They don’t consume added salt. He went on to say:

Unfortunately, the Chinese five thousand years ago discovered that salt had the magic property of preserving food. Salt became of great economic, religious, and political significance, but at the cost of putting up our blood pressure; [it’s also] the major cause of strokes, heart failure, and heart attacks. We are now eating twenty to fifty times more salt than we are designed to.

Again, we are consuming all this salt because it is added into our foods as a preservative or to mask bitter tastes. Preserving food may have helped it last longer, but it had unintended consequences for humans, as MacGregor’s next point shows:

Some of this salt stays in our body and puts up our blood pressure; 60 percent of the population have raised blood pressure at the age of sixty.

The food industry is responsible for 80 percent of our salt intake [which is] hidden in processed foods, fast foods, etc., and they must take responsibility for the thousands of unnecessary deaths and suffering they are causing...for each one gram reduction in salt, approximately six thousand deaths are prevented.

That’s a lot of lives saved! Many packaged foods and drinks contain sodium. Nowadays, salt restriction is taken to mean less than 1600 milligrams per day. That may not seem like much, but remember, our ancestors ate less than 1500 milligrams per day. One might think this alone would be enough to inspire people to cut salt out of their diets. Yet we all know people who eat a lot of salt. My father eats the most salt of anyone in our family, and yet his blood pressure is normal at age eighty-three. Clinical studies have confirmed that the effect of sodium intake on blood pressure is influenced by variations in a gene called angiotensin-converting enzyme (ACE). I decided to find out what variant of the ACE gene I had—GA and AA variants of the ACE gene increase your risk of blood pressure when you eat salt, whereas the GG variant does not. It turns out that I have the AA variant and therefore need to watch my salt intake.

ACE regulates blood pressure in response to salt intake. ACE inhibitors are well-known medications for lowering blood pressure and are used to treat kidney diseases and diabetes. However, we also now know that what variant of the ACE gene you have affects your risk of developing high blood pressure due to salt intake.

In America, the African American population has a much higher risk of high blood pressure, both due to a higher intake of processed food and genetic remnants from the slave-trading era—because slaves needed to survive the difficult trans-Atlantic voyage and brutal conditions of imprisonment while awaiting transport, it is said a slave trader used to lick a slave’s face to assess his fitness for voyage—salty sweat was presumably bad, as it indicated less salt-retaining properties. This taste test was meant to identify good salt-retaining people who were hardy enough to survive the long ocean crossing. However, when these people were chosen selectively for this quality, the African American population ended up with more of these salt-retaining genes and a higher risk of high blood pressure.

I’ve seen a picture of a slave trader assessing his slave thus in a copper engraving by Serge Daget (circa 1725) reproduced by Morris Brown in an article on hypertension and ethnic groups. This “slavery hypothesis” explains the origins of higher blood pressure risk in African Americans—people who were chosen for those salt-retaining properties ended up on the same continent, cohabiting with other slaves, and this resulted in a population with a higher concentration of salt-retaining people. That was in the days before the genome was mapped; however, since we now know that our salt metabolism is determined by our genes, this could be a valid reason why African Americans have a genetic predisposition for high blood pressure. A genetic variation of the MYH9 region on chromosome 22, which is related to kidney disease and salt retention, was found in 74 percent of African Americans and in only 4 percent of Americans of European descent.

And, if you are wondering how much salt you need in your diet, the truth is we need very little. Our ancestors managed with 1.5 grams, and the WHO recommends that adults consume less than 5 grams (just under a teaspoon) of salt per day. These recommendations apply to all individuals, with or without high blood pressure (including pregnant and lactating women), except individuals with illnesses that specifically need sugar replacement or have interactions with sodium-lowering medications such as antidepressants.

Learn more about The Genetics of Health.

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