Why Nutritional Science Is So Confusing

Mar 88 min read

Deciding what to eat has never been more complicated – with endless diet plans, conflicting advice and science that seems to change every week.

Why has it been so difficult for nutritionists to agree on what makes for a healthy diet? And could advances in wearable technology and personalised testing finally offer a definitive answer?

Tuck into my short explainer video to find out more:

Is this healthy?

Imagine you’ve just woken up to breakfast – a bowl of muesli, eggs on toast and a glass of fruit juice. Sounds healthy, right?

Well, it depends who you’re listening to. According to different studies, those eggs are either a protein powerhouse or a cholesterol nightmare. The toast you’ve served them on could be a stable source of energy or a recipe for inflammation. And the muesli? A quick scan of the box confirms they’re packed with fibre and other valuable nutrients. Great. However, the list of ingredients also includes preservatives and flavourings. And, if current thinking on ultra-processed foods is anything to go by, that is a very bad thing.

Lost your appetite? Maybe just have a sip of orange juice (full of essential vitamins but dangerously high in sugar).

When nutrition scientists seem to disagree and routinely change their minds, perhaps it’s little surprise that so many people have been unable to resist the promise of simple answers – however unscientific and unsafe they might be.

A brief history of fad diets

Each year, thousands of books are published promising quick fixes to lose weight and eat your way to a healthier and happier you. Many of their claims are, at best, scientifically questionable. Despite this, in the US alone, one in seven people has followed a fad diet. The pursuit of quick fixes to shed pounds and improve health has taken some bizarre and dangerous turns over the years:

Lord Byron’s Vinegar Diet (1820s): He’s best known as a leading light of the Romantic movement, but Byron can also lay claim to having pioneered the celeb-endorsed fad diet. The poet drank vinegar and water to suppress his appetite. The trend caught on despite causing side effects of nausea and vomiting.
The Cigarette Diet (1920s): Tobacco firm Lucky Strike launched a diet plan with the slogan “Reach for a Lucky instead of a sweet”. In fairness, their claims about the appetite-suppressing effects of nicotine do stand up to scientific scrutiny. But of course, we now know that most of the other health claims made by cigarette companies of that era certainly don’t.
The Grapefruit Diet (1930s): This Hollywood-driven craze recommended eating a grapefruit before every meal and limiting intake to 500 calories per day. It’s gone in and out of fashion over the years as a short-term weight loss plan despite there being no scientific evidence that grapefruit burns fat.
The Sleeping Beauty Diet (1970s): Yes, some people literally sedated themselves to avoid eating. This fad diet became popular in the 1970s and was the subject of a worrying resurgence in 2017.
The Cotton Ball Diet (2013): This social-media craze saw online influencers eating cotton balls soaked in juice as a radical new calorie-free way to stave off hunger. It led to intestinal complications which, in some cases, proved fatal.

Today, you don’t need to scroll your social media feed too far to see TikTok-driven crazes for juice cleanses and adults eating baby food, or influencers using pseudoscience to promote the carnivore diet – where people only consume food derived from animals.

A cartoon image of multiple computer tabs displaying various advice regarding coffee and caffeine.

Contradictory advice

It’s one thing to avoid being duped by the bogus claims of a celebrity-endorsed fad diet (some useful advice on that here). But how can we be sure we’re eating healthily when even the scientists and nutrition experts often seem to disagree?

Why is it so difficult to get a consensus? Is it bad reporting, bad research or something more fundamental?

Let's start with your morning cup of coffee. Depending on where you get your news, it’s either going to increase your risk of heart disease or reduce it. There’s evidence that it’s good for your brain, and also evidence that it’s bad for it.

These contradictory messages sometimes come from the same research. When sensationalist clickbait headlines meet nuanced scientific research, it usually creates more confusion than clarity.

Some believe that the problem goes much deeper than media reporting – it’s nutritional science itself that’s fundamentally flawed. While this field played a crucial role in eliminating diseases like scurvy and rickets years ago, today it struggles to provide clear answers. As New Scientist reports:

There are huge amounts of research on diet published every year, a lot of it funded by governments concerned about rising levels of obesity and diabetes. But even in the pages of respected science journals, we find conflicting results about much of what we eat and drink: potatoes, dairy products, bacon, fruit juice, alcohol, even water. And this isn’t just quibbling over details: there is a major fault line dividing the field over whether we should eat food that is low in fat or low in carbohydrates, for example.

Critics argue that many of the field’s issues stem from its research methods. Since nutritional studies often rely on correlations between diet and health outcomes, they are particularly prone to identifying misleading or coincidental associations. Science writer Amos Zeeberg explains:

Among people who took [one] survey, there were very strong correlations between eating cabbage and having an innie belly button; eating bananas and having higher scores on a reading test than a mathematics test; and eating table salt and having a positive relationship with one’s internet service provider.

Of course, “findings” like these are screened out – it would obviously be ludicrous to suggest any association between salt intake and broadband speeds. But they arise from the same methodology that fuels dubious claims like “Tubs of ice cream help women make babies”. (As Zeeberg explains, researchers were never confident in this finding, and it has largely been forgotten since making headlines in 2007.)

If the traditional way of doing nutrition science is past its use-by date, what’s the alternative?

A cartoon image of an individual reading a list, with bubbles emanating representing broccoli, vitamin C, cheese and other foodstuffs.

This time, it’s personal…

Personalised nutrition companies like ZOE, Viome, and Inside Tracker argue that a good diet plan is not one-size-fits-all.

So, instead of relying on off-the-shelf healthy eating advice, they analyse your DNA and gut microbiome – the trillions of bacteria which play a key role in our metabolism, mood and immune system. Then, using these results plus a whole range of insights gathered through wearable tech, they create a diet plan tailored to you.

Tim Spector, a professor of genetic epidemiology at King’s College London and co-founder of ZOE, argues:

We all have personal tastes and preferences when it comes to food, so it makes sense to assume that our personal metabolisms and responses to the foods we eat should be different too. But we’re only now coming to the point where scientific research is catching up with this gut feeling, proving that everyone is unique and that there is no one true diet that works for all.

That research, led by ZOE, has been billed as the largest nutritional study of its kind – analysing blood sugar, insulin, fat and other markers across 1,100 volunteers, including hundreds of twins.

Spector says some of the findings were striking:

The first thing we noticed was the wide variation in individual insulin, blood sugar and blood fat responses to the same meals, even for identical twins. For example, one twin might have healthy responses to eating carbohydrates but not fat, while the other twin is the opposite. Straight away, this tells us that we are all unique and that there is no perfect diet or correct way to eat that will work for everyone.

The study also found that:

Timing matters – the same meal can have a different nutritional response in some people depending on whether it was eaten at breakfast or lunch. But not for everyone.
Identical twins share only around a third of the same gut microbiome.
Despite the huge diversity of reactions among different people, there was a consistent pattern to how each individual responded to the same meals eaten at the same time on different days.

The implications of this could be transformative in the way we think about nutrition. As Spector puts it: “The take-home message is that there is no one right way to eat that works for everyone, despite what government guidelines and glamorous Instagram gurus tell you.”

Fad or future?

So, is personalised nutrition the antidote to flawed nutrition research and dubious diet trends? Or is it just an expensive, tech-driven fad? It’s undoubtedly more scientifically credible than a celebrity-backed pseudoscience diet. But there’s scepticism about how much of a difference it can make, particularly while the research is still in its early stages.

ZOE markets itself as a "science-first company," but when it published clinical trialresults claiming a wide range of health benefits for participants, it earned a rebuke in the British Medical Journal for overstating the findings.

Advances in wearable technology and home testing kits mean we can collect more data and insights than ever before. But experts believe we lack the knowledge to draw firm conclusions from the data and really distinguish what’s significant.

For instance, our understanding of the microbiome's importance has advanced significantly in recent years. And for some, learning about the billions of bacteria living within us is fascinating. But how useful are these findings when scientists still don’t know what a truly “healthy” microbiome looks like?

Similarly, glucose monitors are invaluable for diabetics, but there’s no consensus that glucose spikes matter much for the rest of us. Nicola Guess, an academic dietitian at Oxford University, says: “I think people are focusing on glucose as a marker simply because we have technology to measure it.”

Or, as the philosopher Julian Baggini puts it simply, perhaps this is just personalising stuff that doesn’t matter.

A cartoon image of a character putting their healthy food shop away in their fridge.

So, what to eat?

Some nutrition advice is timeless. No study is going to conclude that vegetables are bad or that exclusively eating popcorn leads to a longer life. And most of us probably already know we’d benefit from reducing our sugar intake. Often, the key is just getting us to do something about it.

Underpinning the cutting-edge science and gadgets being brought to the table by personalised nutrition is a more traditional approach. These programmes also provide support, education and accountability to help people stick to their personalised diets.

Individually tailored plans for macronutrient balance, meal timing, and specific food responses might one day be a game-changer. But while the science is still in its infancy, support and motivation might be the most valuable things these plans have to offer.

Years before the advent of personalised nutrition, Harvard professor Michael Pollan warned that overcomplicating the study of what we should eat did more harm than good. His answer to the hugely challenging and divisive question of what constitutes a healthy diet? “Eat food. Not too much. Mostly plants.”

To that, we might add: Avoid fad diets and take nutrition study headlines with a (very small) pinch of salt.