Feeding your fitness

Diligently training for a marathon, Barbara alternated hard runs lasting an hour or two with easier jogs meant to give her muscles a break. But the 40-something woman couldn't figure out why those short bursts proved just as taxing as the longer treks, leaving her sore and wiped out.

The pieces came together when Barbara met with Mary Ellen Kelly, a registered dietitian at Harvard-affiliated Brigham and Women's Hospital. To promote fat loss, Barbara confessed, she usually didn't eat after her workouts. But the zero-refueling strategy meant she was sacrificing the strength and endurance she needed to train effectively.

"Those long runs took so much out of her that the shorter runs became incredibly hard, because she was functioning at such an energy and protein deficit," Kelly recounts.

Barbara's example highlights a dramatic distinction between the sexes: after exercise, our bodies require an entirely different approach to replace what's been lost and promote muscle recovery and growth. Optimally, women should refuel within 30 to 45 minutes after a workout, while men have up to three hours to accomplish the same task. Continually ignoring this need can lead to symptoms of low energy availability, such as fatigue and soreness.

As Barbara learned, "it's really hard for the body to optimize recovery if we're chronically under-fueled," Kelly says.

Hormonal drivers

For both women and men, exercise is the best kind of stress, increasing our heart rate and making muscles work harder. But it does require us to nourish ourselves properly to overcome that stress.

That's where the similarities end, however. Why is a woman's refueling window so much shorter? Hormonal variations between the sexes underlie this difference, says Dr. Beth Frates, director of lifestyle medicine and wellness in the Department of Surgery at Harvard-affiliated Massachusetts General Hospital.

Progesterone is a primary driver, exacerbating women's post-exercise muscle breakdown. This outcome is magnified for women who are peri- or postmenopausal. If they allow their muscles to remain in a breakdown state without replenishing with protein — and if they consume protein only at the beginning and end of the day — they're more likely to feel sluggish, sore, and unable to exercise at their peak.

"Women need to refuel with protein more quickly to oppose this breakdown," Dr. Frates says.

During the luteal phase of the menstrual cycle — the week or so before a period arrives — women may also crave more carbohydrates and want to eat more.

"If you feel a little hungrier, it's not in your head — your body actually needs that," Kelly says. "Being mindful of your cycle, listening to your hunger cues, and eating that little extra could support your training."

Protein-packing strategies

Aim to consume at least 70 grams of protein throughout the day so that you begin any workout well-fueled. "That means your muscles have been topped off and hydrated and they're ready to tap into for exercise," Kelly says.

After exercise, you'll want ingest about 20 grams of protein within 45 minutes, and pair it with carbohydrates if you don't plan to eat again within the next hour or two.

Protein-rich food choices include

• a cup of Greek yogurt
• 3 ounces of chicken, turkey, salmon, or steak
• a scoop of whey protein powder
• a ready-to-drink protein shake.

Even a big glass of chocolate milk can provide an adequate mix of the protein, carbohydrates, and electrolytes muscles should ideally receive after exercise, Kelly says.

If, like Barbara, you're aiming for workout-driven fat loss, you can still meet your goal and refuel properly afterward. Just be strategic so you don't sacrifice muscle strength in the process, Kelly says. How? Aim for a calorie deficit at other points in the day, not after your workout time. Kelly suggests monitoring portions and limiting alcoholic drinks.

"If someone is doing a light workout, such as a walk or 20 or 30 minutes on an elliptical machine, the principles of intentional refueling probably don't need to be applied," she says. "But if your workout is intense and your ultimate goal is weight loss, pay attention to your overall fueling patterns."

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