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The Diet Myth | Book Review

Updated: May 5, 2021

An article that investigates how the foods we eat play a roll in promoting good gut health.

a plate with health food, salad and fruit, a diary diet plan

I have read extensively around diet and nutrition and over the years I have amassed a sizeable stack of books on the subject. Most all of these books identify certain food groups within the contemporary diet as the root cause of the current health epidemic that is currently plaguing the West.

For example, the China Study has pinned the rise of cancer on animal protein. How Not to Die, possibly one of the most extensively researched books on diet currently available, also pins cancer on animal food consumption.

But How Not to Die goes much further than the China Study for it claims that all – nearly all – causes of preventable mortality are the direct consequence of a deviation from a ‘plant based diet’.

The Starch Solution is a faint echo of the impressively researched premise that runs through the 400 pages of How Not to Die. However, The Starch Solution suggests that, to restore Western health and banish many of the diseases that are currently killing our civilisation, we should – must – revert back to the primitive diet that formed the staple of Asian farmers; which consists primarily of starch foods and occasionally a choice cut of meat or fish.

The Diet Myth, however, is a refreshing new take on the mercurial and agonisingly elusive reason behind the degeneration of Western health. Tim Spector is Professor of Genetic Epidemiology and for the past two decades he has been studying how our microbes impact on health.

This field of study is currently in its adolescence yet it is yielding some quite fascinating insights into the symbiotic relationship between bacteria and their oblivious host: Homo sapiens. We have known for a hundred years or so that we are not alone, that bacteria live on us and within us (even a clean forehead has two species of lice living on it).

With the rise of technology we have been able to advance our understanding significantly. For example, we now know that trillions of individual bacterium inhabit our intestines. In fact, so densely populated is our intestinal tract that just one cubic square centimetre contains more microbes than all the humans that have ever lived on planet earth – combined!

At first microbiologists – the scientists who specifically study bacterial cultures and their behaviours – thought microbes just lived harmlessly within us (and occasionally not so harmlessly); passive passengers enjoying the ride. But they have learnt that the bacteria living within us do a lot more.

Bacteria aids our digestion by breaking down our foods making them easier to extract nutrients from. And ‘as well as synthesising a third of our own metabolites for us our gut microbes also produce many vitamins,’ (p225/6).

We are not the only species to exploit the humble bacterium. Leaf cutter ants use bacteria to breakdown the leaves they have harvested which enables them to eat the decomposed by-product. It’s an interesting point of reflection to remember that the leaf is actually toxic to the ant before the bacteria re-engineer the molecular structure of the leaf.

However, our relationship with microbes is much more complicated than I have so far discussed. ‘The microbes that colonise humans are highly specialised, possessing pared-down genes to ensure there are no redundant or overlapping mechanisms with the human host. We humans share 38 per cent of occur genes with the microbes inside us. As the transmission of microbes from mother to child is so universal in the animal kingdom, it is clearly crucial for our health,’ (p17).

We’ve been evolving with bacteria for millions of years and it seems that no animal species is an island. When mice are raised in a sterile environment, completely devoid of bacteria, they are weak, sickly and often die prematurely. The research cited throughout The Diet Myth shows that we need our microbes not just to help us digest the next meal but to sustain health and longevity. And it happens that the foods we eat can have the biggest impact on the success of the bacterial cultures that co-inhabit our organism.

the human microbiome and gastrointestinal tract

The central premise of The Diet Myth, if we were to distil it down to its essence, is that human health is largely dictated by our individual microbiota and if it is out of whack we run an increased risk of developing many diseases (see video above). One of the major contributing factors to the recent diminution in the diversity of our microbiome is the blandness of the modern diet.

‘Fifteen thousand years ago,’ says Spector, ‘our ancestors regularly ingested around 150 ingredients in a week. Most people nowadays consume fewer than twenty separate food items and many, if not most, of these are artificially refined,’ (p19). This is quite the paradox when we consider that the average supermarket contains over 40,000 different items half of which are edible. The vast majority of the foods we consume contain just four ingredients: corn, soy, wheat and meat.

Spector prescribes dietary diversification as the best way of promoting a friendly microbiome. ‘It is,’ he reminds, ‘useful to think of your microbiota community as your own garden that you are responsible for. We need to make sure the soil (your intestines) that the plants (your microbes) grow in is healthy, containing plenty of nutrients; and to stop weed of poisonous plants (toxic or disease microbes) taking over we need to cultivate the widest variety of different plants and seeds as possible. I will give you a clue how to do this. Diversity is the key,’ (p20).

a woman preparing a healthy meal standing behind a table with healthy foods

In light of this advice – to diversify our dietary consumption – I decided to log down, over the course of one week, how many different foods I consumed. Though by the end of the week I was way off the extremely diverse diet of my ancestors (150) I was still well above the modern average (20).

In one week I managed to consume 49 different foods and I did not – I should say: fought the temptation to – alter my dietary habits. Striving for greater dietary diversity is fun and the following week to my little experiment I found myself looking for weird and wonderful foods.

Actually, this advice is championed by the author of How Not to Die; though for a different reason. According to Dr Greger different foods contain different cancer fighting chemicals. Avocados fight one type of cancer whereas pumpkins, peppers and broccoli fight another. Thus a varied diet of fresh fruits and vegetables ensures that we ingested a wider array of these chemicals.

But is it just the foods that we eat that impact on the health of our microbiome?

As it happens lifestyle factors can play an important role in promoting or inhibiting friendly bacteria. For example, research has shown that ‘exercise stimulates the immune system in beneficial ways, then the immune system in turn sends chemical signals to the microbes in our gut,’ (p36). So exercise not only reduces our risk factor of developing type II diabetes, obesity and cancer but it also drives positive ‘changes in microbial diversity,’ (p38).

Another lifestyle factor that plays a role in the health of our gastrointestinal gardens is alcohol. Surprisingly moderate alcohol consumption can have a beneficial effect on our microbiome. ‘A detailed sequencing study of the gut microbes of ninety-eight American volunteers found that apart from the effect of body size and dietary fat, the one major dietary factor that had an effect on the composition of our gut microbes was red wine drinking,’ (221).

This is ammunition for anyone who wants to justify the consumption of alcohol as part of a healthy diet. However, I feel that Spector has purposely exaggerated the benefits of wine on our microbiota so as to justify his own predilections. According to Dr Greger ‘moderate drinking does appear to protect against heart disease, perhaps because of a blood-thinning effect, but even light drinking (less than one drink a day) has been found to increase cancer risk,’ ( How Not to Die p144).

In a recent blog Greger stated categorically that the consumption of alcohol in any amount is deleterious to human health. The chemical ethanol, which destabilises cellular mechanics causing that feeling we call drunkenness, is toxic to biological organisms (which might account for why it’s used as an anti-bacterial and steriliser) and it places unnecessary strain on the liver.

The small benefits of consuming alcohol – and there are undeniably some (decrease risk of developing heart disease and the augmentation of microbiome diversity) – pale under the enormous shadow of the myriad ills associated with drinking; such as addiction, cellular degradation, cirrhosis of the liver, genetic damage, cancer (of course), fatty liver syndrome, foetal damage in pregnant woman, obesity and neurological disorders.

"Alcohol consumption contributes to 3 million deaths each year globally as well as to the disabilities and poor health of millions of people. Overall, harmful use of alcohol is responsible for 5.1% of the global burden of disease."

WHO (2020)

I see this as one of the major limitations of The Diet Myth. Spector is so focused on the effects food and lifestyle habits have on the microbiota that he often neglects the bigger picture. An incident of this is where he identifies dairy – more specifically cheese – as fare favourable to promoting and cultivating a diverse garden of microbes.

Yet, The China Study and How Not to Die, both extremely well researched bodies of literature, have fingered out dairy in the line-up of cancer and disease causing foods. T. Collin Campbell, professor Emeritus at Cornell University and author of The China Study, has researched the link between casein, a protein found in dairy, and cancer cell proliferation.

So whilst cheese and other dairy products may promote good bacterial cultures they also contribute to the increase in some of our most deadly diseases.

This reminds me of the smoker who, to justify his habit, cites research showing that smoking reduces one’s chances of developing Parkinson’s by 12.5%, but neglects the statistic that puts the smoker’s risk of developing nine of the ten known lung cancers at 300%.

Irrespective of the many glaring limitations, inconsistencies and contradictions The Diet Myth, on the whole, has much merit to it. The relationship between human health and the well-being of our microbiome is a burgeoning field of research that I feel will prove very important in the fight to reduce ill health.

Maybe one day we’ll be able to ‘hack’ our microbiota and programme them to fight disease or burn unwanted fat or improve our psychological health. Until that day comes, and it very well may not, we must, if we want a flourishing microbial garden, follow the simple advice Spector divulges early on. Diversity is the key.

Below I have compiled a comprehensive list of methods we can use to promote the diversity of our microbiota.


Eat plenty of fresh fruit and vegetables
Eat high quality whole grains
Eat plenty of nuts and seeds and legumes
Drink plenty of fresh water
Fast – or reduce calorie intake. Short term fasting ‘can stimulate friendly microbes, but this is only as long as the other ‘free eating’ days contain a diverse diet,’ (p19)
Exercise daily
Aim to maximise the number of ingredients you consume throughout any given week


Don’t consume meat as it has been shown to alter the composition of our microbiota exacerbating the proliferation of unfriendly species (Greger)
Avoid stress inducing situations
Don’t lead a sedentary life – get up off your arse and move.

If you are interested in a deeper insight of the topic covered see the suggested reading list below. For more information on any of the books click the image!


The Diet Myth: The Real Science Behind What We Eat (click image for your copy)

Why do most diets fail? Why does one person eat a certain meal and gain weight, while another eating the same meal loses pounds? Why, despite all the advice about what to eat, are we all still getting fatter?

The answers are much more surprising - and fascinating - than we've been led to believe. The key to health and weight loss lies not in the latest fad diet, nor even in the simple mantra of 'eat less, exercise more', but in the microbes already inside us.

Drawing on the latest science and his own pioneering research, Professor Tim Spector demystifies the common misconceptions about fat, calories, vitamins and nutrients. Only by understanding what makes our own personal microbes tick can we overcome the confusion of modern nutrition, and achieve a healthy gut and a healthy body.


How Not To Die: Discover the foods scientifically proven

How Not To Die gives effective, scientifically-proven nutritional advice to prevent our biggest killers - including heart disease, breast cancer, prostate cancer, high blood pressure and diabetes - and reveals the astounding health benefits that simple dietary choices can provide.

Based on the latest scientific research, the internationally bestselling How Not To Die examines each of the most common diseases to reveal what, how and why different foods affect us, and how increasing our consumption of certain foods and avoiding others can dramatically reduce our risk of falling sick and even reverse the effects of disease. It also shares Dr Greger's 'Daily Dozen' - the twelve foods we should all eat every day to stay in the best of health.


The China Study

The science is clear. The results are unmistakable. You can dramatically reduce your risk of cancer, heart disease, and diabetes just by changing your diet. More than thirty years ago, nutrition researcher T. Colin Campbell and his team at Cornell, in partnership with teams in China and England, embarked upon the China Study, the most comprehensive study ever undertaken of the relationship between diet and the risk of developing disease.


The Starch Solution

Fear of the almighty carb has taken over the diet industry for the past few decades--from Atkins to Dukan--even the mere mention of a starch-heavy food is enough to trigger an avalanche of shame and longing. But the truth is, carbs are not the enemy!

Bestselling author John A. McDougall and his kitchen-savvy wife, Mary, prove that a starch-rich diet can actually help you lose weight, prevent a variety of ills, and even cure common diseases. By fueling your body primarily with carbohydrates rather than proteins and fats, you will feel satisfied, boost energy, and look and feel your best.


(As we are very interested in user feedback at Hungry4Fitness, I would be very grateful if you could take a few seconds out of your day to leave a comment. Thanks in advance!)

Blog Author

Adam Priest is a former Royal Marines Commando, personal trainer, lecturer, boxing and Thai boxing enthusiast.



Greger, M. Stone, G (2017) How Not to Die; USA; Pan

Spector, T. (2015) The Diet Myth; London; W&N publication.

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