From "calories in, calories out" to "five-a-day" – catchy slogans and advice about food and how to stay healthy are plentiful.

Official government health guidance, nutritionists selling fad diets promising amazing results and companies labeling products with health buzzwords. All offer different and often contradictory messaging around what to eat and how to eat to lead a healthy lifestyle. It can be overwhelming.

Many people complain about having followed diets that friends and even family members have sworn work, yet not seen the same results.

So how much of what's being fed to us, both literally and figuratively, is right for our bodies and based on hard scientific research?

According to genetic epidemiologist and author of The Diet Myth, Tim Spector, not much at all.

"There are many reasons we've got it wrong, a lot of it is trying to think that nutrition was dead simple – and it's probably one of the most complex parts of science – we've just dumbed it down and seen it as not a real science," Spector, a professor at King's College London, told CGTN Europe.

"We have so many self-professed experts in it [nutrition] and very few people actually doing the hard research at the cutting edge," he added.

Spector is part of a team of researchers led by King's College who decided to change that and conduct the largest ongoing nutritional study of its kind, PREDICT, which he says will "change the way everyone thinks about food forever."

In collaboration with the spin-out health science company, ZOE, and researchers across the world, the PREDICT-1 study consisted of 1,103 participants from the UK and the U.S., including 660 identical and non-identical twins. It measured a variety of markers from blood glucose, fat and insulin levels to exercise, sleep and gut microbiome over two weeks, to examine all the different factors that affect people's responses to food together.

No 'one-size-fits-all' in nutrition

"The PREDICT studies show that there's no such thing as an average person – when it comes to food, we're all very different. There's no one-size-fits-all approach to nutrition," Spector said.

The first published results in the Nature Medicine journal showed that many things previously thought about food might not be accurate and that every individual's unique biology should be taken into account, with an emphasis on scientific approaches to achieve a healthy weight.

Researchers explained that the findings showed there was no single "right" way to eat. Even identical twins can respond very differently to the same foods, meaning that, contrary to popular belief, genetics aren't as important as people might think when it comes to food.

As for those generic posters or social media messages prescribing diets based on fixed ratios of fat, carbohydrates, proteins and fiber – researchers say they are over-simplistic and will not work on everyone.

Spector explained: "There's a 10-fold difference in the range of how people respond to identical food. And so, clearly a food label is just not going to work for most people. That's why you picking a diet that your neighbor or friend went on and was successful on, is highly unlikely to work for you."

Eating for our bodies

"We now need to start eating for our bodies. It's not just about genetics, but it's about eating for our microbiome as well," Spector said.

"It's about eating at the right time of day, it's about deciding whether we're the sort of person that's best to exercise before or after food. And it's as much about how you eat, as exactly what you eat," he added.

All of us have gut microbes, which are microscopic creatures, living in our bodies, most are commonly bacteria, fungi, yeasts, and they're also parasites and viruses that feed off everything.

They're essentially thousands of species living in a community, or microbiome, that live off each other and live off the food we put into their environment, producing chemicals for our body, brain and immune system. They keep us hungry or full, they make us happy or sad, and they can help us fight off infections, so scientists say it's important we keep them healthy by putting our gut microbiome at the heart of personal nutrition advice, because it influences your nutritional responses, health and weight.

"We should be thinking much more intelligently of [nutrition] as an interaction of 50,000 chemicals in food, with 100,000 chemicals that are produced by our gut microbes with 1,000s of chemicals in our blood and our brain all interacting together. It's working out what the best combination of chemicals is," Spector explained.

The good news is that the microbiome can be altered by changing what a person eats, giving a positive way for everyone to improve their gut health and weight.

The research also showed that part of eating for our bodies is assessing the inflammatory response initiated by the increase in fat and glucose in our body after eating a meal, which scientists said differs hugely between individuals.

"We learned food itself drives inflammation – and this makes it very hard for us to stay healthy – so when you eat, you get these short-term spikes in sugar levels or fat levels, and that creates inflammation long term," Spector explained. "Which is the real problem and that can lead to all kinds of medical problems as well as weight gain," he added.

So, changing our dietary and lifestyle choices to minimize these prolonged spikes in blood fat and glucose could be a useful target to reduce the potentially dangerous inflammation.

One thing that can help fight inflammation by keeping gut microbes healthy, according to scientists, is fasting. "There's evidence that the longer you leave overnight fasting, particularly more than 12, ideally over 14 hours, actually helps your metabolism and may reduce inflammation," Tim Spector said.

"It's coming down to how we eat, not what we eat, and fighting the idea that there's such a thing as a healthy snack," Spector added.

"Our ancestors didn't have snacks, they basically ate one or two meals a day, and it wasn't very long ago, even perhaps one generation ago, that snacks were extremely rare. So the idea that we should eat six times a day, otherwise we'll faint, is just a modern invention and it's probably very bad for us," he explained.

Food myths

A lot of our eating habits come from cultural norms or advice and fads that have been popularized over time. But not all these habits or nutrition rules that we've been following are accurate or beneficial for us at an individual level.

Spector, who authored the soon-to-be-released book Spoon-Fed, said there are dozens of food myths that are prevalent in most cultures and countries.

"They range from the overriding one about the power of the calorie and the fact that calories are all equal, to specific ones about things like coffee being bad for you because it's a stimulant, therefore there must be something inherently evil about it – and yet it turns out to be good," he explained.

There have been several debates about the concept of "calories in, calories out," which is based on the idea that in order to keep a stable weight, the number of calories you eat needs to be the same as the number you expend. But Spector and the scientists behind PREDICT, say the relationship between the number of calories consumed and nutritional response is not straightforward, and varies greatly between individuals.

Spector said we should "throw out these old ideas about calories" being told by food companies because they love a simple message and "they like to think that just by putting messages like 'low calorie' or 'low fat' on food, they can sell a product and everyone's going to behave the same."

"Other ones about exercise itself helping you lose weight, being a certain myth that's propagated again by the sugar and drinks industry because it makes sense for them to sell more product, to the breakfast cereal industry, telling us all that we must eat breakfast when there's increasing evidence from all these studies that everyone's different and some people really do very well without breakfast," Spector added.

It would be difficult to find many societies and cultures that don't propagate the idea that fish is always good for you and passed it down through the generations. But Spector said that this is one of the dogmas that people need to rethink today because of environmental stresses on the planet.

"Two or three portions of fish a week… is actually unsustainable, and when you look at the data, as I did, you can't see the evidence really for that – fish is pretty neutral, but we simply can't be eating that much," he explained.

There's still a lot of differing opinions between experts themselves about nutrition, and studies found that for about a third of the foods, the top 100 foods, there's no agreement about whether they are good or bad for you.

"Basically a lot of what we're finding is that it's about the quality of food, not about a black and white, yes/no, good/bad," Spector said.
 

The future of food

For the scientists and researchers behind the PREDICT study, throwing out old ideas and myths, and instead carrying out in-depth scientific research in the field of nutrition that takes into account individual human differences, is the way forward, and the future of food.

Though this may seem like a huge undertaking and very complicated to achieve, Spector said that technology in the form of apps and algorithms tailored for each individual is what's needed and will be the future of personalized or precision nutrition.

Apps that would specifically monitor people's individual responses to food and what's good for their gut microbiome would help make informed decisions about what and how we should eat to keep our bodies healthy.

"So, based on our studies, we've come up with a plan that allows you to reduce your dietary inflammation and that helps people lose weight," Spector said.

"And the company that I'm working with, ZOE, has a personalized eating plan now, that's based on your biology rather than calories or macronutrients, and it's not about deprivation, but it's about actually celebrating the many foods that we can all eat and all about diversity," he added.

Video editor: Natalia Luz

Graphics and animation: James Sandifer