Restrictive diets aren’t the secret to staying slim. The key is diversity says Tim Spector, professor and author of the book “The Diet Myth.” Eating foods high in fiber, fermented products and food loaded with micronutrient polyphenols are scientifically proven to improve weight and help the complex microbiome flourish.

“This is where we’ve lost track, we’ve tried to simplify it and we’ve tried to say that calories in equals calories out and that one-size-fits-all and that if everyone has these 2,000 calories a day, they’ll be perfect. And of course, that advice has led to the whole world getting fatter,” Spector says in an interview on webisode Health Hackers. “[People have been taught] erroneous advice that fat is bad for you therefore avoid all things with fat, even healthy things.”

The Health Hackers episode is titled “Why your diet may never work until you get to know your microbiome.” Journalist Gemma Evans interviews Spector in his London research lab. Spector is a professor of genetics at King’s College in London. He has published over 800 research articles, and Reuters ranked him as the top 1% of the worlds must published scientists.

Spector began researching the microbiome seven years ago, when he became sick and wanted to know which diet would help him heal. His early delve into the microbiome fascinated him.

“We hadn’t understood the gut microbiome, which is this whole new organ in our bodies that was previously ignored,” Spector says. “I really got into this whole field and diverted my group’s research interest into discovering more about that microbiome that we all have. We’re all so different in our microbes, and this difference is how we all respond differently to foods and it explains a lot of mysteries.”

Microbiome is a Living Community

Spector describes the microbiome as a living community of trillions of microbes that produce chemicals, vitamins and hormones. Ninety-nine percent of microbes are in the gut, most in the lower gut or colon. Human cells only make up 43% of the human body — the rest are microbe cells.

Healthy microbiomes are full of diverse species. They help avoid overeating or under eating because a healthy microbiome self regulates.

“The healthier your microbiome, the healthier your body is in general because it means that your immune system is being well balanced and not overresponding,” he says. “It’s giving you resistance against its infections; it’s not overreacting to give you allergies.”

Researchers like Spector study the microbes with fecal samples. He says you can tell more about a person and what they’re eating through their fecal matter. Many commercial companies today advertise accurate health measurements by measuring genes through DNA samples.

“As a geneticist, that’s rubbish,” Spector says. “Statistically, it might be true, but actually at a personally level, it’s virtually no use. Our microbes are so much different than our DNA makeup. We share any, for example, 20 to 30 percent of our microbes [between] any two people. And so, understand how that community is and what’s different should mean that I can tell whether someone is healthy or whether they’re more likely to get fat or diabetes, [by] looking at the general diversity [of their microbes]. And I can also try and now use this information when you’ve got thousands of people to predict what the best foods are for people.”

Healthy Eating Myth Busting

It’s fascinating insight into the future of predictive health. Spector’s book, “The Diet Myth,” detailed how the health industry has failed the general public for roughly the past 30 years. People were told to eat low-fat foods, count their calories and get lots of exercise. Spector calls that advice “very old-fashioned, very 20^th Century.”

“We only really understood food around those primitive concepts in these very broad categories of fats and sugars and proteins and we’ve ignored one of the big ones, which is fiber,” Spector says.

Diets cannot revolve around the three blocks of fats, sugar and protein. What matters, Spector says, is the total amount of chemicals consumed and the effects on the body. Take, for example, a banana. A banana can’t be defined in one of the three categories because it’s made up of 600 chemicals. Once a banana is ingested and combines with gut microbes it converts to 6,000 chemicals.

Making the microbiome more complex: everyone will react differently to that same banana. The effects of the chemicals produced will present differently in each individual.

Diversifying Diets — and Microbes

“Virtually all diets, people end up restricting what they eat which actually has a long-term effect of reducing your microbes and therefore they’re less able to cope with modern living,” he adds.

Spector said you cannot generalize healthy eating guidelines with broad generalizations when it comes to the microbiome because everyone will react differently. Human genetics shape the gut microbiome.

“But if you had to have one rule, people on very restrictive diets don’t do well and people who have the more diverse diets…are healthier,” he says. This is because a diverse diet is full of different nutrients and, in turn, build a diverse group of microbes. Spector compares the microbiome to a garden – the nutrients consumed are like the fertilizer helping the plants or microbes grow.

As the head of the Department of Twin Research & Genetic Epidemiology at King’s College, Spector has studied the effect of microbes in twins. In one study, two mice with different weights were analyzed. The overweight mouse with less diverse microbes was given a fecal transplant from his twin, the skinnier mouse with a healthier microbiome. Once that healthier mouse was given the fecal transplant, the overweight mouse continued to lose weight, even when overfed.

“So those microbes are doing a really good job working overtime to convert metabolically to keep that stuff away from going into fat. They’re burning it up in ways we don’t really understand,” Spector says. “Your chances of having good microbes will increase the more you’ve got of them. So the people who have very limited number of microbes, who have very limited diets where they’re just on processed foods, have an increasingly smaller amount of nutrients in there and only a few microbe species like that restrictive species and they elbow the others out and then they can’t react in healthy ways:

Society has to stop demonizing junk food, Spector says, “we have to get away from the idea that these things are so deadly.” Eating a fast-food burger once a year could actually be good for the microbiome, Spector argues, because it will “wake up your system.”

Another study on mice found that mice who consumed lots of fiber (chickpeas, lentils), then were given a high-fat meal didn’t put on weight. Spector said it’s because they had a solid base, and then were given a high-fat meal once in moderation.

Spector is against the concept of clean eating (“There’s no such thing.”) and even processed food (“What’s processed food? It’s cheese. It’s milk. It depends where you draw the line.”). But he says ultra-processed food with harsh chemicals should be kept to an absolute minimum. Ultimately, no one should take a black and white view on food and limit what they eat.

What Should We Eat?

So what should we eat? Spector highlighted four food and drinks that help gut health: foods high in fiber, complex plants, fermented foods and polyphenols.

Fiber is important because it’s what microbes live off. Fiber is hard to digest early in the digestive track, so the nutrients reach the colon before being absorbed. Most ultra-processed foods are so full of sugar that they are absorbed extremely early in the digestive process. Microbes are destroyed by starving them of fiber — microbes can be wiped out if not fed fiber for long periods of time.

Complex plants, Spector advises, prioritizing vegetables first and fruit second. Fermented foods are full of the live bacteria critical for gut health. Spector suggests fermented foods like kefir, yogurt, kimchi, sauerkraut, kombucha, Japanese fermented soy and even quality fermented chocolate. Polyphenols are an energy source for microbes, and can be found in any food like blueberries, raspberries, blackberries, olive oil, dark chocolate, seeds, coffee and green tea.

As far as pill supplements, Spector points out that there’s no scientific evidence yet that probiotic supplements benefit healthy people.

“I’m generally in favor of using food – yogurt, kefir, cheese — rather than expensive supplements,” he says.