Here's how Sports Illustrated swimsuit models stay in such great shape

Sports Illustrated swimsuit models are known for their enviable physiques.

While some, like Irina Shayk, say it's "100% genetic," others work hard to be healthy and toned.

Four of this year's SI swimsuit models tell us the diet and exercise routines it takes to have a bikini model body.

Hannah Ferguson:

"On a good week, I would work out probably five times a week. On a bad week, I probably work out 2-3 times, but it depends on my schedule," Hannah Ferguson tells us.

On a typical day, Ferguson says her eating habits are as follows:

In the morning, I'll usually have scrambled eggs with spinach, and coffee of course. Or fruit and yogurt with some granola. For lunch, I like to have quinoa with chicken or another protein. For dinner, I usually have fish and vegetables. I try to keep my carbs around lunchtime.

But, she warns, "I definitely have a sweet tooth. I'm the kind of girl who, if I have a craving, I'll indulge."

"Ice cream is hands down my favorite food and I do crave chocolate, but I usually try to eat healthy."

Irina Shayk:

While Sports Illustrated's 2011 cover model, Irina Shayk, may joke that "100%" of her good looks is thanks to genetics, the 29-year-old actually works hard for her physique.

"I love fast food, but you have to try to eat healthy," the Russian model told Business Insider on Tuesday at Sports Illustrated's fan festival "Swim City" in Herald Square.

Shayk says that the key to maintaining her weight is not eating late at night.

"Try not to eat after 7 pm, try to stay away from heavy food in the night, like hamburgers and chicken nuggets. Eat that stuff in the morning or early afternoon. If you want to eat chocolate or cakes you have to eat it in the morning, for breakfast or lunch - don't eat it in the night."

Shayk adds that her food intake and workout regimen depends on what city she is in. So, for example, when she's in New York, "it's very easy to eat healthy because you have a lot of organic stores, you have Juice Press."

For workouts, Shayk regularly works out with a personal trainer "because I'm super lazy and cannot workout alone."

In the gym, Shayk tells us, "I don't use any heavy weights, but I do use the weight of my body. I do boxing, pilates, I hate to run but sometimes you have to because it's good cardio. I hate morning workout, I'm a night person more. But it's good to work out in the mornings because then you can have all day free."

But it's not always easy to maintain such a perfect body.

"People think 'She's pretty, she looks good,' but you have to keep it up," says Shayk. "You have to go to the gym everyday. I'm very critical of myself, when I look in the mirror and see cellulite, I have to go workout and get a massage. You have to always push yourself."

Jessica Gomes:

Model Jessica Gomes says a typical, healthy day includes:

Usually I'll wake up, have a smoothie, go exercise, come back and do meetings and have lunch, do a photoshoot, I'll have dinner and then maybe watch a movie. I just like to keep things moving and keep it different. I love swimming, hiking. I love bar classes, I love boxing.

The 29-year-old Australian model says that her workouts are often dictated by her surroundings: "If I'm in New York, I'll go to the gym and box, in Los Angeles I'll go for a hike, in Australia I'll go for a swim. I love being outdoors, I think nature is very healing and I need that."

For her diet, Gomes says, "I keep to a pretty simple thing. I don't eat many carbs. I eat protein, vegetables, I love dairy, though. I kind of look at food as fuel. I like green juices, I love salads. I love delicious, colorful, healthy foods. I don't really drink that much, I'll just have a glass of wine here and there to celebrate."

She says that "dessert is always a big indulgence for me," but that "it's important to not be too strict on yourself because when I'm strict on myself that's when I rebel and that's not good either."

Gomes, who has appeared in the Sports Illustrated swimsuit edition for the past eight years, says that the inclusion of a plus-size model in this year's issue is "incredible."

"I've been so many different shapes and sizes myself, and SI is so embracing of women and being comfortable in your own skin. I think it's incredible that we are embracing curvier women, we should be, it shouldn't even be a topic!"

Kate Bock:

While Sports Illustrated swimsuit models' bodies are important, Kate Bock argues that the models' personalities are equally as important.

"Everyone in the magazine has a different shape from each other, but I think they choose us to be in the magazine based on our personalities, how we speak, how we interact," Bock tells us. "I love SI for choosing girls based on their personality and what they have to offer as well as being a beautiful, beachy, bathing suit, happy person."