“I’m sick and tired of the nutritional nonsense that comes out of the diet industry – it’s an endless parade of quick-fix fads that always sell because they always fail,” he says. “My goal was to stick to the science, create an evidence-based diet book and find every possible tip, trick, tweak and technique proven to accelerate the loss of body fat. It was then a case of building the optimal weight-loss plan from the ground up.”

The aim? By following the science, you only have to lose excess kilos once, then maintain it. No more diets. A promise like that brings the word ‘unicorn’ to mind. Greger and his team didn’t take this quest lightly, combing through 500,000-plus research papers about obesity and slimming down, on the hunt for proven factors that lead to weight loss.

“We came up with 17 elements in food that appeared to independently contribute to weight loss, and a heap of other factors that might also play a role,” he explains. As a WH reader, you won’t be surprised at many of them: watch your sugar and fat intake; go for low-GI foods; eat more fibre. But some are more unusual. So, skip Google and come with us. Your restriction-free, science-fuelled unicorn awaits.

1. When you eat matters

Talk about out morning glory. “Studies show that [kilojoules] eaten first thing cause you to accumulate less body fat than the exact same number eaten at night – and that blew me away,” says Greger. He cites a study, by a team at the Wolfson Medical Center in Tel Aviv, of women on a 5880kJ a-day-diet. Researchers found those who ate 2940kJ at breakfast, 2100kJ at lunch and 840kJ at dinner lost twice as much weight and 5cm more from their waist than a group who saved their large meal for dinner. The theory goes like this: our body uses more energy torching through kilojoules in the AM, leaving less to be potentially stored as fat. Nutritionist Tracie Connor adds, “Eating a smaller meal in the evening also means you’re not consuming energy that won’t get used as you retire for the day.”

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2. Inflammation is a buzz word for a reason

You have a 32 per cent greater chance of gaining weight over the next eight years on a diet high in inflammatory foods compared with an anti-inflammatory one, found a published report in the journal Obesity. How come? Inflammation stops our brains listening to the signals of the appetite-suppressing hormone leptin, reveals Greger. Melbourne nutritionist Anna Block tips, “Reduce inflammation by cutting out processed foods, sugar and anything with additives, pesticides and preservatives.”

3. Salt can get salty with you

Calm down, Salt Bae: analysis of more than a dozen studies found the more of the white stuff people ate, the bigger their waistlines. “We know that salt makes you eat and drink more, but it can make you gain weight in other ways,” explains Greger. “There’s evidence to show that when you switch people to a low-salt diet, levels of ghrelin – the hormone that makes us hungry – in their blood drop.” Want to cut back? Queensland dietitian Amanda Clark tips, “Experiment with herbs and spices for flavour and, if you are eating processed foods, go for low-salt options.” Dig out the soy sauce, too: at Wageningen University in The Netherlands, scientists were able to halve the amount of salt needed in some recipes simply by adding a little of the Asian favourite. You don’t need to use much soy, as its umami flavour brings out the salty taste in food.

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4. There's one kind of "clean eating" we can get around

If by clean you mean limiting pollutants in the foods you eat. Greger cites studies linking the chemical compound Bisphenol A aka BPA, found in plastic bottles and the lining of cans, to weight gain. He also adds that phthalates, another group of compounds in plastic, have been linked to more than 50,000 cases of obesity annually. “I agree with this 100 per cent,” says Block. “Exposure to these obesogenic pollutants alters your hormones, metabolism, energy balance, appetite and cravings. I also suggest my clients avoid them. To limit your exposure, cut back on plastics and prioritise clean, organic whole foods, sustainably caught seafood, grass-fed, pasture-raised meats and drink natural spring water stored in glass.” Also consider buying brands that use BPA free cans. In a 2011 study, a Harvard team tested BPA levels in people eating a daily serve of homemade soup for five days, then retested them as the group had canned soup for the same period. The latter scenario drove a 1000 per cent rise in BPA levels compared with the group’s time on fresh food. Wow!

5. There's a magic number

Let’s chat about a little something called energy density – basically, a measure of how many kilojoules per gram a food contains. The idea is, by choosing foods with a low-energy density, you can enjoy more and feel full, yet still cut kilos. Greger suggests going for options that contain a sweet spot of 147 kilojoules per 28 grams, as per advice from the American Institute for Cancer Research. Frontrunners: fruit such as bananas and avocado, vegetables, whole grains, legumes (beans, lentils, chickpeas), yoghurt and seafood. At the back of the line: meat, poultry, eggs, bread, dried fruit, along with chips, chocolate and oils.

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6. Your gut bugs take centre stage

We know you hear it a lot, but your gut bacteria really are the Beyoncés of the health world – multitalented AF. And weight control is part of their set list. “Feed a group of people the same 10,080 kilojoules and then analyse their stools,” says Greger (we’ll take his word on that one), referring to a 2011 study by the US National Institutes of Health. “While some retain 9870 of those kilojoules, others only keep 9240. It’s because of the different types of bacteria in their guts.” Clark nods to the influence of gut bugs on kilo count, too. “There’s still much to learn but research definitely supports a link,” she says. “If you want to improve gut flora, the clearest evidence is that eating lots of fibre breeds the best diversity. Plus, it gives you an extra advantage [because fibre-rich foods often have] low-energy density.”

7. Plants rule all

Greger’s team found one diet plan that ticked off all 17 of the weight management elements. Drum roll, please: it’s eating plant-based. “Often confused with being vegan or vegetarian, this just means you emphasise foods from plant sources over other foods,” Greger says. “It’s the most effective dietary intervention ever published in terms of weight loss over six to 12 months.” We’re talking about maximising your intake of whole plant foods, including fruits, vegetables, legumes, whole grains, nuts, seeds and herbs and spices. Block suggests, “Make these the main feature of your meals – playing around with textures, colours and variety – then, a few times a week, add some sustainable fish, pasture raised eggs or grass-fed meat as an accompaniment. It’s that easy.” OK, experts, you’ve got us – that doesn’t sound like a diet. Or, if it is, it’s one we’ll happily come back to.