By Dr. Mercola
What you eat can either add to or take away from your exercise benefits, and if you're devoting the time to working out, you want to know how to harness your meals to support your efforts, not detract from them. Choosing the proper foods is important, but so is the timing of when you eat them.
Men and women are different in this respect, according to an experiment featured on the BBC's "Trust Me I'm A Doctor" program. Women who exercise, for instance, may be able to burn 22 percent more fat just by tweaking the timing of their meals.
Women May Burn More Fat by Eating Before Exercise; Men by Eating After
In an experiment of 30 men and women by Adam Collins, Ph.D., nutrition consultant and senior lecturer in nutrition at the University of Surrey, participants took part in three fitness classes a week (high-intensity training, Zumba and spin class).
They consumed a drink — either a caloric carbohydrate beverage or a zero-calorie placebo beverage — before and after class.
Women burned more fat overall than men, but the women who consumed the carbohydrate drink prior to exercise burned up to 22 percent more fat. Among men, however, those who consumed the carbohydrate drink after exercise burned up to 8 percent more fat.1
The discrepancy likely has to do with the body's preferred source of fuel. Men tend to have more muscle, where carbohydrates are stored, making this their preferred fuel. Women, on the other hand, may burn fat more readily in order to conserve carbohydrates. Collins told the Daily Maill:2
"Women have more fat around hips, bums and tums, better release of fatty acids into the blood, hormonal differences which mean they can be better and more frugal at conserving glucose [sugar from carbohydrates] and burning fat.
'This is probably an evolutionary advantage to do with pregnancy. If women are better at managing their fuels they have glucose to spare for the fetus.'"
Women May Want to Avoid Eating for 90 Minutes After Exercise
When men exercise in a fasted state, they limit their source of carbohydrates as fuel, which means the muscles may then burn more fat. Women, however, tended to burn the most fat in the three hours after exercise.
Because of this, Collins recommended women avoid eating for at least 90 minutes after exercise. If you women choose to eat in this timeframe, it provides the body with carbohydrates to burn, which means your body may not shift into beneficial fat-burning mode.
Men, however, can eat after exercise and still maximize their fat burning.3 It should be noted that this study only looked into the effects of consuming carbohydrates — not proteins and/or fats. It would be interesting to see if the results differed depending on the types of foods consumed.
If You're Fat Adapted, You Need Very Little Carb Replacement, Even During Exercise
If you've been following a low-carb, Paleo-style diet, or a high-fat, moderate-protein, low-carb diet like the one described in my nutrition plan, your body is probably fat adapted.
Our ancestors were adapted to using fat as their primary fuel, but over 99 percent of Americans are now adapted to using sugar or glucose as their No. 1 fuel source instead.
One way to tell if you're fat adapted or not is to take note of how you feel when you skip a meal. If you can skip meals without getting ravenous and cranky (or craving carbs), you're likely fat-adapted.
Being able to rely more on fat for energy during exertion spares your glycogen for when you really need it. This can improve athletic performance and helps burn more body fat.
As explained by former Ironman triathlete Mark Sisson, if you can handle exercising without having to eat carbs first, you're probably fat-adapted.
If you can work out effectively in a fasted state, you're definitely fat-adapted. Replacing non-vegetable carbs with healthy fats, and fasting intermittently, are among the most effective ways to encourage your body to change from burning carbs to burning fat.
So for those of you already following a high-fat, low-carb diet, you're likely quite efficient at burning fat for fuel and will require very little carb replacement even during intense exercise.
If you're a competitive athlete, there is some evidence that switching to a higher-carb diet just before a race (after you've been on a low-carb diet) can help to "top off your tanks" to boost your performance, but this is highly individual.
For many, this strategy may backfire, as the sudden carb consumption may lead to headaches, nausea, bloating and other symptoms as well.
What Are the Benefits of Exercising in a Fasted State?
The featured study suggests men do best exercising in a fasted state, which for many simply means exercising first thing in the morning, prior to breakfast. For women, you may want to listen to your body and monitor your fitness goals to see if this is a beneficial strategy for you as well.
When you exercise while fasting, it essentially forces your body to shed fat, as your body's fat-burning processes are controlled by your sympathetic nervous system (SNS), and your SNS is activated by exercise and lack of food.
The combination of fasting and exercising maximizes the impact of cellular factors and catalysts (cyclic AMP and AMP Kinases), which force the breakdown of fat and glycogen for energy.
On the other hand, eating a full meal, particularly carbohydrates, before your workout will inhibit your sympathetic nervous system and reduce the fat-burning effect of your exercise.
Eating lots of carbs activates your parasympathetic nervous system, (which promotes energy storage — the complete opposite of what you're aiming for).
One study found, for example, that fasting before aerobic training leads to reductions in both body weight and body fat, while eating before a workout decreases only body weight (this study included only men).4
Beyond Fat Burning: Reasons to Exercise While Fasting
Exercise and fasting together also yields acute oxidative stress, which actually benefits your muscle trigger genes and growth factors. This includes brain-derived neurotropic factor (BDNF) and muscle regulatory factors (MRFs), which signal brain stem cells and muscle satellite cells to convert into new neurons and new muscle cells, respectively.
This means that exercise while fasting may actually help to keep your brain, neuro-motors and muscle fibers biologically young. The combined effect of both intermittent fasting and short intense exercise may go way beyond helping you to burn more fat and lose weight; it may help you to:
✓ Turn back the biological clock in your muscle and brain
✓ Boost growth hormone
✓ Improve body composition
✓ Boost cognitive function
✓ Boost testosterone
✓ Prevent depression
This strategy would probably not be appropriate for long endurance exercise, but for the vast majority of casual exercisers, it can be quite beneficial. One of the easiest ways to do this for most people is simply to exercise before eating breakfast, as you've been fasting since your dinner the night before.
One exception to fasting before exercise is if you are doing strength training. When you are fasting for 14 to 18 hours you typically deplete most of your glycogen stores, which makes it difficult to lift your maximum weight to failure.
Hence, if you are doing heavy lifting to failure, you may want to avoid training while fasting. In these cases it is likely helpful to consume some healthy slow-releasing starchy carbs the night before working out so your glycogen stores won't be depleted in the morning.
Then, have whey protein as a pre-exercise meal to grant sufficient supply of branched-chain amino acids for optimum muscle fueling during your workout.
What Are the Best Foods to Support Your Workouts?
As noted by sports nutritionist Susan M. Kleiner, R.D., Ph.D, "When it comes to sculpting your body and enhancing your performance, without a diet to support your training you are wasting your time in the gym."5
The best food for your workouts depends on your personal and fitness goals, health status and possibly your sex as well. However, in general fitness expert Ori Hofmekler recommends flooding your body with stress-activated food nutrients (SAF nutrients) prior to exercise, as these nutrients mimic the effects of intermittent fasting and exercise. He explains:
"Once ingested, SAF nutrients demonstrated the capacity to increase animal and human survivability. Some of these nutrients have shown to mimic the anti-obesity, anti-diabetic, and anti-aging effects of exercise and fasting on the body. The point is, food rich in those exercise-mimicking nutrients is ideal for pre-workout. Not only that it can prevent setbacks with the fat burning and healing impact of exercise, it may actually enhance that impact.
… Note that some of the most potent SAF nutrients are no longer part of our diet. These hard-to-find nutrients occur in barks, roots, pits, and peels, which we don't normally eat. However, some foods within our reach contain high levels of exercise-mimicking SAF nutrients such as phenols, caffeine, theobromine, catechins, and immune proteins and thus can potentially yield powerful synergy with physical training."
Try Eating This Before Your Workout
Exercising while fasting may work for some people, but if you find it difficult to exercise on an empty stomach then SAF nutrients may be optimal for you. So where are these nutrients found?
- Whey protein from grass-fed cows
- Organic black coffee
- Unsweetened cocoa
- Green tea
Take, for instance, a study published in the journal Medicine and Science in Sports & Exercise. It demonstrated that consuming whey protein (20 grams protein/serving) 30 minutes before resistance training boosts the body's metabolism for as much as 24 hours after your workout in both men and women.6
It appears as though the amino acids found in high-quality whey protein activate certain cellular mechanisms (mTORC-1), which in turn promote muscle protein synthesis, boost thyroid, and also protect against declining testosterone levels after exercise.
I believe the best approach is to use some common sense and listen to your body. If you feel weak or nauseous while exercising on an empty stomach, you may want to eat a small meal, such as a high-quality whey protein shake, as mentioned, before your workout.
Should You Eat Breakfast on Non-Exercise Days?
Should your morning routine include a healthy breakfast? Conventional nutritional dogma states that breakfast is the most important meal of the day, but if you're not a fan there's no harm in skipping it, as skipping breakfast extends the natural time of your overnight fasting period.
This type of intermittent fasting has numerous benefits for your health. That being said, if you enjoy breakfast and feel better when you eat it, it can certainly be part of a healthy morning routine. Examples of breakfast foods that include healthy protein are organic pastured eggs (soft boiled, poached or raw), a whey protein smoothie, or leftovers from a healthy dinner.
You don't want to consume too much protein either, but when your breakfast contains a moderate amount, research shows it alters signals in your brain that control food motivation and reward-driven behavior, making it a potential strategy to reduce reward-driven eating behavior and potentially help with weight loss.7
The key to remember is that your body probably only needs two meals a day, and eating this way allows you to restrict your eating to a window of six to eight consecutive hours each day, and avoid food for at least three hours before bedtime.
As long as you restrict your eating to a six to eight-hour window, and avoid eating for at least three hours before bed, you can choose between having breakfast and lunch, or lunch and dinner, but avoid having both breakfast and dinner. Which two meals you prefer are up to you; let your body, and your lifestyle, including your workout schedule, be your guide.