Miranda Kerr's personal trainer reveals the one diet that made his models gain weight

New York-based Victoria's Secret model trainer Justin Gelband may not agree with London's fitness fads, but he was impressed with the local food scene on a recent visit to the capital.

"The food [in London] is better than in America," Gelband told Business Insider.

Gelband trains some of the most famous Victoria's Secret models, including Miranda Kerr, Candice Swanepoel, Irina Shaik, Karlie Kloss, and Martha Hunt.

In June, he spent two weeks teaching at BXR London, a luxury boxing gym in Marylebone.

Though exercise is central to his brand, Gelband said that body maintenance is not just about working out. "85% percent of what you do is what you eat," he said.

Gelband does not recommend juice diets as a way to lose weight. (iStock)

Many nutrition experts have stressed the importance of healthy eating habits as a faster way to achieve your fitness goal than simply focusing on exercise.

"In order to lose a kilo of fat you would probably have to run two marathons," Michael Mosley, author of the "5:2 diet" and the "Clever Guts Diet," told Business Insider in a video interview. "In many ways it is obviously much easier simply to reduce the amount of calories you eat rather than trying to run them off because you have to do so much exercise to burn calories."

There is no one-size-fits-all diet, Gelband admits, though he's a fan of the Paleo Diet, also known as the "caveman diet." The regime is mainly based on foods that were around in the stone-age, such as fruit, vegetables, roots, and nuts.

On the other hand, the Victoria's Secret model trainer is cautious about juice-only diets, especially if people are using juicing as a method to shed pounds.

"At Fashion Week some models went on a juice diet and didn't tell me," Gelband said. "Not one lost weight, some actually gained weight. That got me in big trouble."

​In a typical juice cleanse or diet, you dramatically reduce your calorie intake, which can lead the body to hold onto to extra calories.

Registered dietitian Ilyse Schapirohe told Eat This: "Once you stop eating enough food to meet your basic energy requirements, your metabolism will slow. For most people, that threshold of calorie intake is around 1,200 calories per day.

She explained that at this point your body goes into conservation mode -- or starvation mode -- because it doesn't know when its next meal is going to be. Going too low for too long, like more than a couple of days, can have the opposite effect, Schapirophe told the website. In this mode your body can start clinging on to every calorie it can get.

"There's a time and place for juice fasting -- just not for weight loss," Gelband said. "If you're on a yoga retreat in Bali, you're meditating and doing yoga and you want to drink juices because you don't want any heavy foods in your body, that's fine," he added.

Gelband said he has "a gift" for whipping Victoria's Secret models into shape, but that he "makes them eat. "Food is key to energy," he said. "They're not bean poles."

For fitness inspo, or just to watch him work his magic on some of the world's most famous supermodels follow him on Instagram @justingelband4u.

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