A pair of twins followed different diets for 12 weeks. The high-carb twin lost more fat and had more energy.
Hugo and Ross Turner followed a high-fat and high-carb diet, respectively, for 12 weeks.
The identical twins both got fitter and leaner, but Hugo said he 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, professional adventurers who live in the UK, have previously tested the effects of 40-minute workouts versus 20-minute workouts and compared 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 whether 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 the brothers could maintain their already high levels of strength and fitness during the experiment, rather than lose fat or build muscle, sports scientists at the UK's University of Loughborough monitored them.
While Hugo, who was 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, who was 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 expedition 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 about 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 a day: Hugo with more fats and Ross with more carbs.
Hugo followed Frive's low-carb meal plan and added high-fat foods such as 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 nonnegotiable.
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 9 calories per gram whereas carbs (and protein) contain 4. So you can eat more carbs for the same number 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. Others, however, 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'd 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 the brothers agreed that 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 compositions.
On the high-fat diet, Hugo:
Gained 3 kilograms (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 in 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%
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, noted that "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 was notable that both twins saw improvements in cardiovascular fitness and metabolic health.
But the high-carb diet appeared to help Ross 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 probably 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 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, such as cycling, running, or kite skiing, they would up their carbohydrates beforehand. Conversely, if they were doing a walking expedition or something slower-paced, they'd choose a higher-fat diet, they said.
Correction: February 6, 2025 — An earlier version of this story misstated how much muscle Hugo Turner gained during the experiment. He gained 3 kilograms, not 1 kilogram.
Read the original article on Business Insider
