The next time you see a weightlifter preach the value of a low-carb high-fat diet, remember that low-carb works for low activity.
The average bro spends most of his time sedentary. They may work out hard for the half hour or hour or so they are at the gym, but other than maybe a few minutes of walking on the treadmill or elsewhere “for cardio”, they’re not burning much of any carbohydrates.
So of course it makes sense for them to preach low carb dieting. The reason high carb diets have produced obesity is because people consume a lot of carbs they don’t use. We’re sedentary, yet people consume hundreds of grams of carbohydrate a day suitable for someone physically active.
If you’re a runner or a triathlete, meanwhile, you likely are endurance training over longer periods of time, and your body draws on available glycogen stores, which can only be replenished through carbohydrates.
Sure, there is a whole other discussion around the value of a metabolic reset by avoiding carbs for a period, or carb cycling (eating lots of carbs around training and relatively few carbs when not), and taking it easy on carb intake when not training or during an extended recovery period. And, in some endurance training situations (ultrarunners can vouch for this), a low carb diet and “fat-adapting” may be more useful for training than consuming large amounts of carbs.
But for most athletes, a carb-rich diet is less harmful and more important to you than any benefits from a lower-carb higher-fat diet.
That said, as always, focus on whole foods (fruit, vegetables, nuts/seeds, meat) rather than packaged and processed foods. The quality of your food matters as well.