by Dr. Krutika Nanavati
We’re often told that if we feel tired, we just need to eat better, sleep more, or train smarter. But what if you’re already doing all those things and still feel off?
Many people who live active, health-focused lives experience unpredictable energy crashes, brain fog, and difficulty recovering from exercise. These issues are usually brushed off as overwork, stress, or a “busy schedule,” but for some, there’s a deeper metabolic reason the body isn’t bouncing back the way it should.
I recently met a 24-year-old long-distance runner who had been struggling with this exact issue. His training was consistent, his hydration was dialed in, and his meals were what most would call textbook clean carefully portioned, full of lean protein, oats, fruits, and supplements. On paper, everything looked perfect.
Still, his energy was unstable. He felt strong during workouts but drained the rest of the day. He relied on snacks to get through the afternoon and described a kind of constant internal restlessness like his body was always one step behind.
This wasn’t a burnout. It wasn’t under-eating. What we found was something many active individuals are starting to encounter: low metabolic flexibility.
Metabolic flexibility is the body’s ability to shift between using carbohydrates and fats for energy based on what’s available and what’s needed. When this switch isn’t working well, your body relies heavily on glucose and struggles to access stored fat. That means when you run out of carbs between meals, your energy drops fast.
In this runner’s case, his body had become so dependent on carbs that even minor gaps between meals left him foggy and fatigued. It wasn’t a diet quality problem, it was a lack of metabolic training.
We didn’t introduce any extreme changes. He began by rebalancing his meals, reducing ultra-processed “fitness” snacks, and adding more whole food fats and proteins. A few of his morning runs were done before breakfast not to burn fat, but to retrain his body to function without constant carbohydrate input. Slowly, his metabolism started to respond.
Within three weeks, he noticed fewer energy dips and more stable moods. He wasn’t reaching for snacks constantly. By the sixth week, his recovery had improved, and so had his endurance. What stood out most wasn’t a faster sprint or a bigger lift, it was the steadiness he described: “I’m not in survival mode anymore. I finally feel balanced.”
What this taught me and continues to remind me is that nutrition isn’t just about what you eat, but how your body responds to it.
Metabolic flexibility doesn’t require a restrictive diet or a complicated plan. It develops from small adjustments in how we eat and train allowing the body to become more resilient, not just more fueled.
If you’re eating well, moving often, and still feeling like your energy isn’t matching your effort, this might be the system that needs attention, not your willpower, not your workouts, and not your calorie count.
His problem wasn’t what he ate, it was how his body was using it.
Metabolic flexibility refers to the body’s ability to shift between burning carbohydrates and fats for energy. In his case, that shift wasn’t happening efficiently. His body had grown too used to quick carbohydrates and wasn’t accessing stored fat when needed. As a result, even short periods without food led to dips in energy, focus, and mood.
We made a few practical changes. He started eating protein- and fat-rich breakfasts instead of relying on carbs alone. He cut back on processed “health” snacks and focused on whole meals. Some of his lighter training sessions were done without eating beforehand not to push limits, but to help his body relearn how to function without constant fuel.
After a few weeks, he noticed that his energy felt more stable. He didn’t need to snack as often, and his recovery between workouts improved. He described it simply: “I feel more even throughout the day.”
The goal wasn’t to follow a trend or adopt a strict diet, it was to help his metabolism become more responsive. For people who are already eating well and training regularly, this kind of shift can make a noticeable difference. Energy isn’t just about eating more, it’s also about how well your body adapts between meals, between workouts, and under stress. That’s what flexibility looks like on a metabolic level.
About Author
Dr. Krutika Nanavati is a Registered Nutritionist and Dietician with the Nutrition Society of New Zealand. She holds a Ph.D. in Sport and Exercise and works closely with athletes and active individuals to improve performance, energy stability, and recovery through personalized, evidence-based nutrition strategies. Through online doctor consultations, she helps clients across the globe access expert nutrition guidance tailored to their unique health and performance goals.