There's a saying in the world of fitness, that "you can't out train a bad diet" and that certainly seems to be the case for the "fittest woman in the world." Katrin Davidsdottir, who was the winner of the 2015 CrossFit Games, has revealed exactly what she fuels herself up with while she is training, and if we're being honest, it doesn't sound that difficult. As we all know, building strength and physical fitness is about much more than just lifting weights and going for runs in the gym. While these activities undoubtedly help you get into better shape, the key part of getting is what you eat. So what does Katrin eat? [[instagramwidget||https://www.instagram.com/p/BcKfHZrDLKa/?hl=en&taken-by=katrintanja]] Well, for breakfast, Katrin starts with three eggs, fried on both sides, half an avocado, fruit and a coffee with cream. Speaking to Women's Health, Katrin says that breakfast is key to her having a good day. "I've got to have my eggs, otherwise my day starts off wrong," she says. "In an effort to get more fat in my diet for fuel, I eat half of the avocado and then the cream in my coffee." For lunch, the 24-year-old tends to have chicken salad with the other half of the avocado she used at breakfast. "I'll eat as soon as I finish training, and leave practice drinking coconut water with a scoop of chocolate protein powder and a serving of fruit. For dinner, I try to eat lots of dark green stuff-spinach, kale, broccoli. For protein, I'll have chicken. For dinner, which would come soon after that late lunch, I try to eat a portion of salmon for its healthy fats and vitamin D." [[instagramwidget||https://www.instagram.com/p/BcH7DKEDNI2/?hl=en&taken-by=katrintanja]] So, plenty of protein, fats and fibre are the key to Katrin's diet. But what does a dietitian think of it? Brigette Zeitlin, R.D., and dietitian at B Nutritious, says that Katrin diet measures up pretty well. "For anyone upping their training frequency, they need to make sure they are increasing their protein intake (goal 25 to 30 percent calories from protein a day) and carbohydrate intake (goal 30 to 35 percent calories from carbohydrates a day)," she says. "The carbs will give your body fuel and the protein will help build and repair muscle tissue." "I like that Katrin is eating high-quality proteins at each meal, definitely a must for someone with her training schedule," says Zeitlin. "[Veggies at dinner are critical] because they are a great source of fibre and fuel. I tell my clients to aim for two to three cups." [[instagramwidget||https://www.instagram.com/p/Bah-izAjAEL/?hl=en&taken-by=katrintanja]] It seems like it's not really that hard to eat healthy - chicken, salmon, eggs and veggies are all pretty tasty. But, while it may seem easy, the biggest killer of a good diet is the temptation to gorge on the likes of pizza, chocolate and ice cream. Despite being the "fittest woman in the world", Katrin admits that she does give in to temptation every now and then: "If I'm craving something, it'll be something sweet," she says. "My food is pretty clean because that's how I want to eat. I do like my chocolate and cake every now and again. I definitely have my sweet tooth." Pretty simple stuff, right? I might follow Katrin's example and become the "fittest man in the world." Or, on the other hand, I might just order a Dominos.

You’ve fuelled up your day with the best breakfast for fat loss and have pretty much stayed on track all day. But come home time and you’re tired, on the edge of hangry and can’t give a single F to cook.

The decision you make here - what to eat for dinner for fat loss - could make all the difference with your ultimate goal and the never-ending "Why am I not ripped yet" complaining. Succumbing to that Papa John's temptation is not going to help, so maybe try one of these dinners from some top nutrition experts.

1. Watercress and rocket salad

No this isn't just leaves on a plate. Of course we want this salad to keep you full until breakfast (or at least bedtime). “Opt for a good source of plant-based protein and green leafy vegetables,” says Michela Vagnini, nutritionist at Natures Plus. “I would suggest a watercress and rocket salad with avocado, olives, sprouted beans, chickpeas and sunflower seeds. You could add extra organic tofu cubes if you need more protein or are feeling tired and rundown. "For a dressing mix lemon juice, coriander, thyme, a pinch of salt and extra-virgin olive oil, or serve with a dollop of hummus for flavour.

"This plate is a perfect post-workout meal if you are vegan and trying to lose weight as it is low in simple carbs and high in healthy fats, so it is a great way to keep your insulin levels stable and stimulate fat breakdown for energy production.”

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2. Black bean and quinoa salad

This vegan option (like the first one) is championed by David Wiener, training and nutrition specialist at fitness app Freeletics. “Beans are incredibly low in fat and calories, but are packed with protein and healthy fats, while quinoa is an amazing, diet-friendly grain that is filled with protein to keep you feeling fuller for longer, and stop you overeating. Your salad can also include as many vegetables as you like and be tailored to your likes and dislikes, so try adding broccoli, chilli, asparagus and avocado to make it really filling, and delicious too.”

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3. Teriyaki tofu with wholegrain rice

“Teriyaki tofu served on a small bed of wholegrain rice,” says Liam Mahoney, Grenade nutritionist. “This is a really easy and low-fat dish for mid-week meals when you can’t be bothered to cook. Tofu is a great source of protein, high in iron, calcium, the minerals manganese, selenium and phosphorous, and it contains all eight essential amino acids. Essentially, it’s so nutritionally satisfying it will reduce the risk of snacking later in the evening.”

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4. Stuffed Portobello mushrooms

Wiener offers another late night winner. You can’t go wrong with mushrooms. They’re fat free, low in calories, and rich in antioxidants. To make this a filling dinner you can stuff the mushrooms with spinach, mixed peppers, onions and just a sprinkling of cheese for added flavour. They’re also delicious hot or cold and can be served with a salad or vegetables such as sweet potato, which is full of fibre and nutrients which can help you burn fat.”

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5. Spicy grilled chicken and stir-fried spring greens

“When you are coeliac, you would normally stay away from highly refined/junk foods as they often contain some form of gluten,” says Vagnini. “Boost your fat loss even more with a dish that’s great for increasing the metabolism: serve grilled chicken, marinated with chilli or harissa sauce, with stir-fried spring greens. Chilli has a thermogenic effect and studies have shown that the consumption of chilli can help in accelerating weight loss through dietary modifications.”

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6. Mexican cauliflower rice

“One of my favourite meals is Mexican cauliflower rice,” says Weiner. “Using cauliflower instead of regular rice is useful for keeping carb and calorie levels in daily guidelines when you don't have time to weigh out items. Mix it with onions, jalapeno’s, crushed tomatoes and a healthy lean protein source such as chicken breast or white fish.”

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7. Miso-grilled salmon, sweet potato and broccoli

“I would recommend miso-grilled salmon fillets with sweet potato and broccoli,” adds Mahoney. “This is a delicious way to get in the healthy fats that your body needs, as well as giving you a good source of carbohydrates and fibre.”

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8. Tuna steak with a fennel

“Go for a tuna steak with a fennel, avocado, shaved coconut and grapefruit salad,” says Vagnini. “Tuna and other oily fishes contain omega 3 fatty acids that could regulate leptin, a hormone which directly affects your metabolism’s choice to store calories as fat or burn them off. For a dressing, use ginger and pumpkin seed oil. In recent studies, ginger has shown a possible modulating effect into obesity through various potential mechanisms, including increasing thermogenesis, inhibition of intestinal fat absorption, and controlling your appetite.”

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9. Courgette spaghetti with walnuts

“Courgette spaghetti with basil, parmesan pesto and chopped walnuts,” says Vagnini. “This recipe is full of good fats, healthy protein and fibre to keep you fuller for longer and maintain a healthy gut. Parmesan cheese made from grass-fed cows contains conjugated linoleic acid (CLA), a natural fatty acid found in meat and dairy products. Cows and other pastured ruminants such as goats and deer have a unique enzyme in their digestive system that converts the omega-6 fatty acids in green plants to CLA. Research has shown that CLA reduces body fat in animals by increasing the amounts of specific enzymes and proteins that are involved in fat breakdown.”

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10. Chicken stir-fry with egg noodles

“Trying to be healthy when you can eat anything can be incredibly challenging, as you will often find yourself stuck for choice and opt for the unhealthier option,” says Mahoney.  "You could make yourself a delicious chicken stir fry with egg noodles, to give you a satisfying feeling whilst eating healthy and getting a sufficient amount of vegetables in your dinner. It’s rich in protein - both from the chicken and the egg noodles, which are also a much healthier alternative to white rice.”

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It doesn't have to involve hours of slaving away or making something Instagramable. Whipping up a nutritionally balanced, hunger pangs squashing meal is surprisingly easy - whatever your foodie preferences or needs.

Halle Berry is 52 years old, but she doesn't look it. But it's not worth getting down on yourself too hard for not looking the same, after all she is a celebrity. That means she has no worries about money, no time wasted on the morning and evening commute to and from work, and has the dollar to spend on personal trainers and personal chefs to make her diet as streamlined as possible.

But what exactly does she eat?

The actress has been open about following the keto diet in the past, and frequently shares stories about the food she eats and her exercise regime on Instagram, but now, Peter Lee Thomas, her personal trainer, has come forward with all the details. Thomas spoke to Hollywood Life, where he revealed all that she eats in a day.

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First of all, she doesn't eat anything for breakfast - instead having a large glass of water (about 8-12 oz) with a squeeze of lemon. Before you all run away at the prospect of no breakfast, let's check out the rest of her routine. Before her workout, she takes amino acids to help her build muscle.

Check out Halle Berry in truly bad*ss action in the video below:

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"Essentially it is the actual amino acids that build muscle, not the actual food source, because the food first needs to be converted into amino acids to create the muscle," Thomas said. "If you imagine your body as a freeway system, these amino acids go straight onto the freeway. It's the quickest way possible for your body to get these nutrients because nothing has to be digested."

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After this, she has a coffee, with one or two tablespoons of MCT oil. This oil (medium chain triglycerides) can be found in coconoil oil, Ghee, and certain types of butter. Adding oil or butter to your coffee is known as a 'bulletproof coffee' - with some in the health industry saying it speeds up fat-burning and others saying it just adds calories.

Following this, she sometimes takes a pre-workout supplement, usually 'Can't Beet This' - which is made from beetroots and contains natural caffeine. After her workout, she has her first real meal of the day - basically brunch. Berry has a nutrient-dense meal to recover, usually steak or chicken with dark leafy greens like spinach or kale, and often two or three eggs.

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Over the course of the day, she snacks on various fruits and vegetables. "She always has lots of cut up veggies around and it's great because the kids like to snack on that too," said Thomas. "She likes blueberries, strawberries, raspberries, and blackberries, those are all good on the ketogenic plan."

Aside from her love of snacking on organic vegetables and fruits, she also drinks bone broth whenever she feels like it in the day - sometimes even in bed. "A lot of the times you can go to a butcher shop and they will literally give you free beef bones and buffalo bones and chicken bones, because they just don't want them and they'll give them to you for free and with that you can make a really nice bone broth," Thomas said.

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Then, for dinner, her chef (Cristina Shabatian) makes her a lamb stew. "She really likes lamb so she'll often have a lamb chop or her chef will make her a really nice ketogenic stew, that will have a lot of cauliflower and broccoli and other vegetables that are filling and some sort of lean grass-fed protein in it," her personal trainer added.

For her final meal of the day, she will sometimes alternate this with 'zoodles' (zucchini noodles) with pesto and pine nuts. Otherwise she'll instead have a ketogenic chilli con carne - which is basically chilli without the beans (sorry to all the veggies out there).

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While this clearly works for Berry - it's not possible for everyone. And even if you can pull it off, it's worth mentioning that different people can respond to diets in different ways, so no rigid routine will work for all people in the same way.

Serena Williams is undoubtedly one of the greatest tennis players who ever lived.

There are few who have combined her incredible fighting spirit, will to win and mastery of the technique of the game to such an extent. In fact, she may well be in a league of her own in that regard.

Serena has won an astonishing 23 grand slams in her career - an open era record - and is second only to Margaret Court (24) in the all time singles majors list.

It may be hard to believe, seeing as she has barely seemed to age a day during her years in the spotlight, but Serena is now 38 years old, and has a child, daughter Alexis Olympia Ohanian Jr.

Yet the tennis champ is still serving looks off the court, and recently took to Instagram to share some vacation snaps with her millions of fans.

Check out Serena's rock hard abs in the video below:

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The 38-year-old tennis ace also shared some other snaps from the Yacht break, much to the delight of her fans.

Gigi Hadid wrote simply, "Yes." while others flocked to the comments section to praise the mom for her awesome snaps.

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So how does she maintain her incredible physique? Well, through her enduring commitment to being one of the foremost athletes in the world, obviously, but Serena has previously given us some clues on what she eats, too.

She told Bon Apetite;

“Everyone loves my roasted chicken with garlic; for a minute, it was my turkey tacos. Now it’s vegan sushi. I just love to cook!”

Per Yahoo, she also advised that she keeps many healthy options in the fridge, such as coconut water, ginger, loads of veggies and wheat grass.

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Yet despite all this, and her incredible physique, Serena says she hasn't always been full of body confidence. She told ESPN's The Undefeated;

“There was a time when I didn’t feel incredibly comfortable about my body because I felt like I was too strong, then I had to take a second and think, ‘well, who says I’m too strong?’

“This body has enabled me to be the greatest player that I can be.”

And that is, without doubt, one of the greatest tennis players of all time.

Jenna Jameson has revealed everything that she eats in a day to maintain her toned physique.

The former adult movie star has regularly kept her followers on social media up to date with her weight loss journey, and now she has made good on her statement from last month that she would be getting "back on track" with her keto diet.

Jameson shows off her incredible body while stepping out of a pool: 

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"Here's my first #keto menu for my fellow people that are on this journey with me!" the former adult movie star and fitness enthusiast wrote while posing in a Baywatch-esque red bathing suit.

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Jameson explained that her breakfasts consist of one cup of coffee and two eggs with "hot sauce and arugula wrapped in Parmesan Folios cheese wraps."

Then, for lunch, she will have zucchini noodles with "a touch of butter with salt and pepper," followed by a Korean beef bowl for dinner.

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"I sauteed cauliflower rice in a pan and then in a separate pan I fry up hamburger then add crushed giner [sic], coconut, aminos, garlic and sesame oil," she explained in the caption. "I top the cauliflower rice with the hamburger blend and then sprinkle green onion...and joila [sic]! It's so hearty and filling!"

Jameson revealed in December that she had readopted the Keto diet after gaining 20lbs.

"Confession. I've gained 20 pounds. Ugh. I decided to take a break from #keto and live my best carby life," she wrote on Instagram.

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"The weight came back fast and furious," she revealed. "I know a lot of people are quitting keto because it's hard to maintain and after a year and a half I concur. Not sure if I’m going to go back full force or just calorie count."

Jameson has been a big celebrity proponent of the keto diet which she first adopted in March 2018, almost a year after the birth of daughter Batel Lu in April 2017.

JLo has a sick body. And in other news, the sky is blue. But it’s still easy to feel blown away when the singer posts a photo flaunting just how jacked she really is. You could spend hours on Jennifer Lopez's Instagram. Her abs (and legs, and butt, and arms…) have the power to suck you in and make you wonder: how the hell can this woman keep looking better, year after year? The answer: a whole lot of hard work and a pretty strict diet.

The latest evidence: A new Instagram she shared to celebrate her 49th birthday. “Current birthday situation…yup,” she captioned a shot of herself, her boyfriend Alex Rodriguez, and a few other pals clutching bottles of bubbly on the beach.

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Jennifer Lopez turned 49-freaking-years old, and she’s got a serious washboard situation going on. J.Lo is well-aware that her stomach looks good, too, because she shared a photo on Instagram right before that of herself at the gym in skintight pants and an abs-baring sports bra. At this point you're probably just waiting to read what she eats, I will tell you but let's just look at one more pic.

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Delicious. Anyways here's the nitty gritty. For one, her meals never include processed food. On top of that, almost everything Lopez eats is organic. A typical lunch might include salmon and a salad that's packed with veggies. Broccoli, peppers, and zucchini drizzled with vinaigrette is a fave, as is kale with crumbled queso and toasted pumpkin seeds.

Come dinnertime, she'll switch up the protein - "I like pork and chicken, especially Puerto Rican style!" she told UsWeekly - and enjoy it with quinoa or baked yams. Nothing boring about that right. I could eat this at least four times a week. Plus you may not be buying these from the exact same store as J.Lo but these items are readily available.

When she's not eating, Lopez's got a regular show at Planet Hollywood in Vegas, she stars in NBC's police drama Shades of Blue, and she's a judge on the new dance competition show World of Dance. All this to say, girlfriend is always on the go. It can be really easy to reach for a bag of Cheez-Its, but Lopez knows better. "I always have healthy snacks, like fruits and vegetables, with me," she revealed to People.

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When Lopez finally does indulge, it's not with black bean brownies trying to masquerade as the real deal. The singer's new boo, Alex Rodriguez. revealed on The View that her guilty pleasures are chocolate chip ice cream and chocolate chip cookies.

We all have our vices - avocados, chocolate, unicorn anything and everything — but Lopez doesn't indulge in any of the usuals. "I don't drink or smoke or have caffeine," she told UsWeekly.

On the rare occasion that she does indulge in coffee, it's always decaf. Keeping her complexion clear is also a big reason JLo cites for skipping caffeine and alcohol: "That really wrecks your skin as you get older."

Nothing out of the ordinary here, just hard work and listening to your body. Go JLo! See you in 30 years when you finally look 29.