Workout performance remains a top concern for bodybuilding legend Arnold Schwarzenegger. In Arnold’s Pump Club newsletter from June 2, 2026, he broke down whether staying on a keto diet wrecks your training results.
“Cutting carbs doesn’t drag down your performance across the board. But it can create real limitations when you’re pushing your body to its limits.”
During the Golden Era, Arnold Schwarzenegger amassed seven Mr. Olympia titles, proving himself as one of the greatest bodybuilders of all time. At 78, his training looks different from what it was. Instead of pursuing hypertrophy and mass, his focus has shifted to mobility and longevity.
Dieting also changed for Schwarzenegger in retirement. He chooses to eat a mostly-plant-based diet to maintain his heart health. He sparingly uses carbs and explains below whether one of the most popular forms of dieting can hinder workout progress.
Arnold Schwarzenegger Shares Whether Keto Diets Sabotage Your Training
In the newsletter, Schwarzenegger pointed to 13 studies on carb restriction. They found that single max effort changes were minimal, but repeated hard efforts showed some decline in performance.
“A new meta-analysis compiled 13 studies on carb restriction and short, intense efforts in competitive athletes aged 18 to 45. Single max efforts (one jump, one heavy lift, one short sprint) held steady without much of a change. Repeated hard efforts appeared shakier, with declines in performance in some studies.”
He explained that the most common discovery was that lactate dropped for those on a low-carb diet.
“The most consistent finding was more clarity about what’s happening inside your body when you cut carbs and exercise. Lactate dropped reliably on a low-carb diet, and understanding this change can help you determine whether low-carb is the right move for your fitness goals.”
Schwarzenegger compared our muscles to a series of engines, which can run fast or slow, depending on carb intake:
“Picture your muscles as a series of engines. The instant engine powers all-out efforts up to about 10 seconds. It appears it’s less dependent on carbs, which is why single max efforts survived carb restriction.”
“The fast engine handles hard bouts of roughly 10 to 60 seconds, especially repeated ones, and it runs on carbs stored in your muscle. Starve it, and it can’t keep firing, so repeated sprints are the soft spot. Or higher rep workouts. Lactate is the exhaust from that fast engine. Burn fewer carbs, make less of it. For years, that lower lactate has been sold as proof of a “cleaner” metabolism.”
Interestingly, he pointed out that power often held up despite less lactate.
“The plainer reading is the right one: your carb-burning engine is running less, not running better. And here’s the wrinkle that should keep you skeptical of tidy stories in either direction: power often held up even as lactate fell, so a low number isn’t proof your engine can’t make force.
So what do you do with this? If you like how you feel on low-carb, you don’t have to let a study change what’s working for you,” he added. “But the research suggests carbs are performance fuel. If your training is mostly steady-state, the vulnerable zone isn’t yours, and there’s no reason to fear or chase low-carb.”
Most notably, he shared that keto diets may affect performance on high-intensity interval training or sports like basketball and soccer. However, resistance training told a different story. He revealed that one-rep max strength was preserved, but higher-rep workouts could suffer.
“If you do intervals, HIIT, or stop-and-go sports like basketball or soccer, chronic carb restriction may dull your ability to repeat hard efforts: fine on the first round, flat by the fifth.”
“Lift heavy for low reps? Single max strength looked well preserved. A hard hour workout with higher reps, focused on building muscle? You might be holding back growth.”
For optimal results, Schwarzenegger said to time carbs around harder workouts.
“If you want to limit carbs — and the research does not suggest you need to (carbs do not make you fat, excess fat does) — the strategy the scientists suggest is matching carbs to the day, more around your hard sessions and fewer on easy ones. Fuel the work, don’t fear the carbs.”
Keto diets, or meal plans moderate in protein, with low carbs and high fats, absolutely have merit. However, Schwarzenegger warns that certain types of workouts can be affected.
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