Nutrition & Recipes

What’s the best diet for exercise?

By Fiona Bugler • 27th May 2020

Started to exercise hard? Feel fitter, healthier – and hungrier? What is the best diet to keep you fit and to help you stay in shape?

Do you carb up, or go keto, eat meat or choose vegan?  John Berardi, of Precision Nutrition has the answers.

Food is the fuel that you need to fire your fitness engine, so make sure you get the right balance of energy and nutrients is vital to help turn you into a lean, mean, running machine. Remember, nutrition is not overly complicated, check out our five simple rules.

Buy how finely-tuned does your engine need to be? What’s the right fuel combination to keep you performing well — and if you’re trying to lose weight, what will keep the pounds off?

John Berardi, PhD is a founder of Precision Nutrition, the world’s largest online nutrition coaching company. He’s an author, professor, coach and all-round nutrition expert. See his profile here.

Macronutrients Don’t Matter

In short, Berardi points out that all diets and eating plans when followed, work. They all have their pros and cons, and they all have evangelical advocates. If you know people who follow a particular way of eating, you probably have seen them have success. There are slim, fit and super healthy vegans, meat-eaters, high carb and low carb eaters, fasters and people who eat all day long.

All diets and eating plans when followed, work

So does it really matter whether you have more carbs, fat or protein? Is the macronutrient mix the key ingredient to success? What’s better low carb or high protein?

The science categorically, says no, it really doesn’t matter. In 2013 The Journal of American Medical Association (JAMA), revealed that: “numerous trials comparing diets differing in macronutrient composition has demonstrated…very small and inconsistent differences in weight loss and metabolic risk factors.”

Stick at it: adherence counts

And furthermore, the real difference, the key to success for most diets is simple. It comes from sticking at it. Again in JAMA, four meta-analyses summarising between 14 and 24 major trials (in another words a broad sweep of studies) found that “adherence is the only consistent factor with weight loss and disease-related outcomes.”

To Carb Or Not To Carb?

But surely when you exercise, it’s different — we need carbs right? Why would we have all those pasta parties, energy gels and sweets if we didn’t? Or is the movement for ‘train low (carb), race high’ the right approach? And with leading figures in the running world, such as Tim Noakes, author of The Lore of Running having a complete about-turn, saying carbs are not good for runners should we ditch the pasta, the porridge and the wholegrain bars for all exercise?

“As a rule, I think it’s worth pointing out that those who are following the low carb diets and preaching that carbs are bad for you are generally coming from the mouths of hyper disciplined, type-A people,” says Berardi.

“Ask yourself what do you prefer to eat? If you’re running well, and you’re healthy and you’re eating the things you want why change it?” he adds.

The high carb diet and endurance

So how does the ‘traditional’ cardio exerciser’s, in particular, endurance exerciser’s diet work? “The high carb diet has an internally consistent system,” explains Berardi. “You deal with the blood sugar swings that are inevitable from having a high carb/high sugar diet, by taking gels and sugary drinks when you train — the system fixes itself,” he says. “But if you don’t do all of it, problems will show up, so for example, if you don’t have gels in a longer race, you may underperform. You think it’s because you didn’t have a gel. It’s not. It’s because you eat a high carb diet and you didn’t have the buffer when you needed it,” he explains. “If you’re going to use the high carb diet and you’re healthy and performing well, then that’s good, but you have to use the whole system,” he adds.

Go high fat?

And what about the new approach? The new school of physiology and nutrition which says you should choose a high-fat diet, which is “glycogen sparing”? The theory goes that you train the body to use fat when you run. You burn fat during your training and events and therefore you do not have to be always loading up with carbs.

“If you eat a high fat and low carb diet theoretically you shouldn’t burn and crash. When you run a race like a marathon, you burn more of your calories as fat so if you eat more fat in your diet, there should be a delay in tapping into your glycogen stores,” explains Berardi, “For most athletes, the liver can hold 100 to 120g carbs and whole body carb storage is around 400 to 600g or 1600 to 2400 calories (but remember the exact total amount depends on body size and muscle mass),” he adds.

Eat for body type

Berardi concludes that you really have to choose what works for you — your tastes, your preferences, but his and other’s research does point to guidelines on eating for your body shape (see them at 

Most runners and endurance-type athletes are ectomorphs (skinny, longer limbs) and according to his research, they are better able to metabolise carbohydrates than other body types, and should aim to have a diet that consists of around 55 per cent carbs, 25 per cent protein, and 20 per cent fat.

For a mesomorph (stockier and athletic in a muscular way), it’s 40 per cent carbohydrate, 30 per cent protein, and 30 per cent fat, and for the rounder, heavier endomorph, Precision Nutrition recommends around 25 per cent carbs, 35 per cent protein, and 40 per cent fat.

Fine-tune your macronutrients

But, as mentioned at the beginning of this article — macronutrients aren’t really that important, for most of us. And, Berardi points out that the fine-tuning of macronutrients is most relevant for elite runners. “Recreational runners and exercisers — i.e. those who run or workout two to three times a week — should not eat differently than someone who is eating for health. You don’t need to carb up. You don’t even need to take carbs in a workout,” says Berardi.

Eating for health is as always, about eating less processed, healthy food, “a mixture of proteins and carbohydrates and fats,” says Berardi.

The best diet balance

1. Protein: Try lean chicken, fish and eggs for a daily protein fix and snack on nuts, and seeds for smaller protein hits. Protein not only repairs muscle damage, but it also helps to feel full. Whey protein is one of the most popular and research-supported proteins for athletes and is often found in recovery drinks.

2. Carbs: As a rough guide, you need around five to 10 grammes of carbohydrate per kilogram of body weight per day. Choose pulses (which also are protein-rich) and whole grains. For a simple ‘rule’ opt for brown — bread, rice, pasta. And don’t forget that you can get carbohydrates from a diet rich in colourful fruits and vegetables.

3. Fat: Eat healthy fats. Choose foods rich in ‘natural’ fat: butter, milk, cheese, eggs, meat, fish, avocado, nuts, seeds, olive oil. And remember saturated isn’t all bad. Recent research has found that the risk of CHD in country’s where saturated fat was high was less than in the country’s where processed high sugar dominated.

4. Water: Stay hydrated. As well as drinking lots of water, throughout the day, an antioxidant-rich smoothie or juice (made with dark berries and vitamin-rich fruit) is the multi-tasker way to fill up fast! Eat water-rich foods, like watermelon, apples, lettuce etc.

Handy portion size control

Don’t count calories — for the best diet balance, use your hands to measure out portion sizes. Berardi recommends the following:

  • Your palm determines your protein portions.
  • Your fist determines your veggie portions.
  • Your cupped hand determines your carb portions.
  • Your thumb determines your fat portions.


Add in extras?

Check out i-wellbeing’s recommendations: 

Four Sigmatic coffee

Athletic Greens

Kombucha Health Shots

Fiona Bugler

Fiona is the creator of all things editorial, she’s a journalist with a life-long passion for health, fitness and wellbeing. For more than a decade she worked with business leaders and large groups as a personal trainer and running coach and this background informs the content she creates.

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