- The twins Hugo and Ross Turner followed a high-fat and high-carb diet, respectively, for 12 weeks.
- They both got fitter and leaner, but Hugo lacked energy on the high-fat diet.
- A sports scientist advised eating a balance of carbs and fats that fits with your lifestyle.
A pair of identical twins who followed different diets for 12 weeks both got fitter and leaner regardless of whether they ate high-fat or high-carb — but the high-carb twin had more energy.
Ross and Hugo Turner, 36, a pair of professional adventurers based in the UK, previously tested whether 40-minute workouts made them twice as fit and lean as 20-minute workouts, and their muscle mass and chronic disease biomarkers after eating vegan and omnivorous diets, respectively.
They asked their 25,000 social media followers what to try next and it became clear people wanted to know if a low-carb or low-fat diet was "better" for strength, fitness, and aesthetics.
While some people, such as keto diet devotees, swear by going low-carb and high-fat to hit their goals, others argue that cutting fats is the route to results.
To determine whether they could maintain their already high levels of strength and fitness during the experiment, rather than lose fat or build muscle, sports scientists at the University of Loughborough, UK, monitored them.
While Hugo, on the high-fat diet, gained more muscle than his brother, he told Business Insider he performed worse and felt more fatigued during intense exercise. Ross, on the high-carb diet, didn't put on as much muscle but lost a little more fat and performed better in cardiovascular tests. The twins now plan to tweak what they eat depending on what expediton they're on.
The experiment was anecdotal and not large enough to prove which diet is "better." But a sports physiologist who worked with the brothers told BI it was interesting that both got fitter.
The twins added 500 calories of carbs or fat to their diets
Before the experiment, both Hugo and Ross balanced carbs and fats in their diets. For the experiment, they ate around 3,500 calories each day, 2,500 from three meals and two snacks from a food delivery service called Frive.
They didn't want to go to extremes so made their diets nutritionally different by only 500 calories per day: Hugo from fats, and Ross from carbs.
Hugo (on the high-fat diet) followed Frive's low-carb meal plan and added high-fat foods like olive oil, butter, nuts, eggs, and avocado. Meanwhile, Ross followed a "balanced" meal plan and added calories from high-carb foods such as pasta and rice, while avoiding high-fat foods.
To support their training, they also consumed 350-calorie protein shakes each day. Keeping your protein intake high is important for muscle building and repair, so was a non-negotiable.
The Turners did similar workouts featuring a mixture of cardio and strength training, using home gym equipment, and rested every three days.
"We weren't perfect with our training but we weren't perfect together," Ross said.
The low-carb and low-fat diets felt restrictive
Hugo said he found the high-fat diet "incredibly difficult" mentally and didn't feel energized or motivated.
"I just never felt good," he said. "I was eating at least six times a day and never felt full or satisfied, hence I was constantly hungry. But equally, I didn't have the crashes that I would probably associate with a higher-carb diet."
Hugo said the high-fat diet felt relatively repetitive and he missed feeling full. Fat contains nine calories per gram whereas carbs (and protein) contain four. So you can eat more carbs for the same amount of calories as a smaller portion of high-fat food.
For this reason, some people don't feel so full on a high-fat, low-carb diet. However, others find they don't feel satiated without consuming a decent amount of fat.
Ross said he missed the mouthfeel of high-fat foods, but felt full. He would occasionally have a small piece of dark chocolate, which helped with the cravings a little.
"I had my first piece of cheese in 12 weeks yesterday, and it tasted insanely good," Ross said after the experiment, and they agreed were really looking forward to eating pizza.
Endurance exercises were tougher on the high-fat diet
Before and after the experiment, the Turners measured their body composition.
On the high-fat diet, Hugo:
- Gained 1 kilogram (6.6 pounds) of muscle
- Lost 0.3 kilograms (0.6 pounds) of fat
- Gained internal (visceral) fat: increasing from 11.4% to 12.6%
- Saw no change to his cholesterol levels
On the high-carb diet, Ross:
- Gained 1 kilogram (2.2 pounds) of muscle
- Lost 0.9 kilograms (two pounds) of fat.
- Lost internal (visceral) fat: decreasing from 11.5% to 11.1%
- Lowered his cholesterol
The Turners also tested their strength and fitness, including documenting changes in their bench presses, VO2 max, and back squats, among other exercises.
They both got better results on the strength tests by almost the exact same amount, but Hugo (high-fat) lacked energy in the cardiovascular fitness and endurance tests.
"Around 40 minutes into the running I felt like I was completely done," he said. "It felt dreadful."
Data collected by the researchers backed up Hugo's feelings: By testing their lactate thresholds while running (which involved taking blood pricks from their ear lobes every 10 minutes), they could see Hugo was struggling. Blood lactate correlates with how hard someone is working metabolically.
Ross, who was able to run for longer by the end of the experiment, said: "Carbs are very good and readily available for providing the body with energy at higher intensities."
There's no such thing as the 'best diet'
Steven Harris, a performance physiologist at Loughborough University who worked with the Turners, said it's notable that both twins saw improvements in cardiovascular fitness and metabolic health.
However, the high-carb diet appeared to help Ross to push himself slightly harder, possibly during his 12 weeks of training and not just the final tests.
While detailed breakdowns can be helpful for elite athletes, Harris advises the average person to eat a balance of carbs and fats that makes them feel their best and fuels their lifestyle, rather than copying what others say is the "best" diet.
Generally, if you know you're going to do a tough training session, you'll likely perform better if you've got some carbs in the tank, Harris said, which aligns with what other nutrition and sports experts have previously told BI.
While the Turners both prefer eating diets with a balance of protein, carbs, and fat day-to-day, they said they might tweak their diets before particular expeditions going forward.
For example, ahead of high-intensity activities that raise the heart rate a lot, like cycling, running, or kite skiing, they would up their carbohydrates beforehand. Conversely, if they were doing a walking expedition or something slower-paced, they would choose a higher-fat diet, they said.
