Eating to Support Physical Activity

Whether you are a weekend warrior, dancer, athlete, or recently-active ex-couch potato, it can sometimes be a challenge to eat so that you feel strong and energetic, yet not bloated, crampy, or nauseous.

The key to eating well for activity is to eat enough, but not too much before the activity, hydrate before, during, and after activity, replace electrolytes, and get enough carbohydrates.  There are different ways to accomplish these goals, and you will want to experiment with what works for your body and sport.

This blog is intended to give you a brief overview of eating/drinking to support physical activity – it is not a comprehensive treatise on the subject.  There are a couple of books on Sports Nutrition that are affordable and accessible and I strongly recommend these if you are an athlete or dancer who competes (or performs).

Nancy Clark’s Sports Nutrition Guidebook, 4th Edition, 2008, Nancy Clark, MS, RDThis is a resource for active people.  Nancy Clark has a loyal following of athletes and dietitians – her approach to eating for sport is within the context of healthy eating for overall health.  Book also includes easy-to-prepare recipes.

Advanced Sports Nutrition, 2006, Dan Benardot, PhD, RD, FACSMThis is an easy-to-read textbook for coaches and professionals working with athletes.  There is a lot of information about Nutrition for various sports.  I appreciate the level of detail.

Sports Nutrition:  A Practice Manual for Professionals, 4th Edition, 2006, American Dietetic AssociationThis is a very useful reference for health professionals (especially dietitians) or seriously geeked-out non-professionals.  Book includes a chapter on disordered eating in athletes.

Position Statement of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine:  Nutrition and Athletic Performance, 2009This is a journal article that gives a succinct summary of the hot topics.  This link should allow you free access to the PDF file.

 

Macronutrients

Protein, carbohydrate, and fat are macronutrients in foods and drinks that provide calories that our body needs to perform work.  We need all three to be well nourished, and with the exception of certain disease states, the Institute of Medicine finds that most adults will do just fine if the percentage of calories coming from each macronutrient falls somewhere within these ranges:

Carbs:        45 – 65%

Protein:      10 – 35%

Fat:            20 – 35%

Notice how large the range is for each macronutrient – there is not one “right” amount to be dictated to all individuals in a group.  This implies that there is quite a range of eating patterns can support good health.

For athletes, Benardot recommends that carbs should be closer to 55-65% of total calorie intake.  The reason will become clear in the next section.

 

Intensity Dictates Preferred Fuel Source

The intensity of activity determines the body’s preferred fuel source (fat, carbs, and phosphocreatine system) at the time of activity.  Specifically, the rate at which ATP (Adenosine Triphosphate) needs to be produced determines which energy metabolic system will be used.  Think of ATP as the ultimate energy currency of cells.

Ø  At lower intensity levels, the body prefers to oxidize fat for energy as the major fuel source.

Ø  At higher intensity levels, the body prefers to use stored carbohydrate (muscle glycogen) as the major fuel source as it can be utilized without oxygen.

Ø  At maximum (peak) intensities, the body will rely on production of ATP from stored phosphocreatine (does not require oxygen either).

Most athletes and dancers who compete at high intensities for prolonged periods will be using stored muscle glycogen to fuel much of their activities.  The occasional burst of peak intensity (think of a flip in the air or high jump) will use the phosphocreatine system.  Walking around, stretching, shaking the legs out – these are lower intensity level activities so the body will use fat as the primary fuel source.

 

Carbs – We Need ‘Em

If you engage in high-intensity physical activities then you want to insure that your diet includes plenty of carbs (as mentioned earlier, 55 – 65% of total calorie intake) so that you can maximize muscle glycogen storage.

Another way to think about adequate carb intake is number of grams per kilogram (kg) of body weight.  To determine your weight in kilograms simply divide your weight in pounds by 2.2 (e.g. 135 lbs/2.2 = 61.4 kg).  According to The American Dietetic Association (ADA) in “Sports Nutrition, 4th Edition,” the typical U.S. diet provides about 4 – 5 grams carbs/kg body weight/day.  The recommended daily intake for trained athletes ranges between 5 – 7 grams/kg body weight/day for general training, and up to 7 – 10 gram/kg body weight/day for endurance athletes.  Endurance activities are those that are higher intensity and continuous for 90 minutes or longer (e.g. shoe shopping for 90 minutes does not count as an endurance sport).

 

Before Exercise

Carbs are also useful to eat before activity as they help prevent low blood sugar.  Carbs are typically “easy to digest” in the sense that they pass from stomach to small intestine in a reasonable time period and then get absorbed into the blood stream.  The timelier this process is, the more comfortable you will be in terms of eating for activity.  Gastric emptying is the term that we use to describe this timely passage.

Carbs are sugars, starches (complex carbohydrates) and fibers.  The Utah Education Network has a detailed lesson plan on carbohydrates that also serves as a good detailed summary – check it out if you have time.  The type of carb that will be best for you to eat before activity will depend a bit on you, but for the most part, a combination of sugars and starches is usually well tolerated.  Here are tips that I had to learn the hard way:

·         Too much sugar (think smoothie) can cause a large amount of water to enter the small intestine and can cause bloating, cramping and possibly diarrhea.  For the chemists out there, foods/drinks with a high osmolality will be more likely to do this.

 

·         Carbs that contain too much fiber can cause bloating and possibly slow gastric emptying – so it might be uncomfortable to eat these before activity.  I find that I do fine with carbs like Breakfast cereals that contain 5 grams of dietary fiber or less if I eat within an hour of exercise.  You might find that you can go as high as 10 grams, and others might have to limit their fiber to 3 grams or less before exercise. Experiment with different levels of fiber and keep a log – that way, you’ll know what you can tolerate.

 

·         Carbs that have a lot of added fats are not going to be as easily tolerated as lower fat carbs.  For instance, French fries might not be as comfortable as say, a bowl of oatmeal, plain potato, or plain toast.  High fat content will slow gastric emptying – so don’t skip the pasta or rice – just avoid the fatty sauce or fatty meats.

 

·         In general, watch portion size before activity.  Something might be well tolerated in a small portion size, but make you feel rotten if you eat twice as much. 

 

·         According to Nancy Clark, MS, RDif you eat 1 hour before an event, then limit your intake to about 1 gram carb/kg body weight.  For a 135 lb person (64.1 kg), that would be 64 grams of whatever carbs you tolerate best.   A sample breakfast that I might eat would be 1 cup of Cheerios (20g) + 1 Activia (yogurt) (19g) + 1 medium banana (27g).  If you have about 4 hours before an event, you might be able to consume up to 2 grams carbs/kg body weight, keeping in mind to avoid high fat foods.

Some protein, but not too much, is usually well-tolerated, especially if the source is low fat.  You will have to figure out which sources you can tolerate before exercise.  Eggs make me feel nauseous before exercise, whereas yogurt or part-skim mozzarella cheese is perfect.  Usually, 10-15 grams of protein works for me.  Ordinarily, a meal would provide closer to 20 – 30 grams of protein if I didn’t worry about timing with exercise.

If I am feeling light headed or hungry before my workout, despite not having skipped my last meal, I’ll eat about 25-30 grams of carbs with about 5-10 grams of a low-fat protein (e.g. ½ cup OJ, 7 crackers, and 1 low fat string cheese or 1 Zone bar) and then wait about 20 – 30 minutes before exercising.  I do not recommend trying to “tough it out.”  Starting a work-out with low blood sugar will typically mean poor performance, a work-out cut short, and possibly a relentless headache during and after the activity.

According to the American Dietetic Association’s Position Statement on Nutrition for Athletic Performance, drink about 5 – 7 milliliters water /kg body weight within 4 hours of the activity to optimize hydration and allow enough time to urinate.  For a 135 lb (64.1 kg) person, that would be 320 ml – 450 ml, or, about 10 - 15 fl oz. 

 

During Exercise

If you exercise for more than 60 minutes continuously, in addition to water, you are likely to enhance performance if you ingest 100 – 200 Kcal of carbs (25 –50  grams) for every hour after the first hour  This is where regular Gatorade can come in handy, or the sports gels.  Some research shows that products that include a little protein might also help performance after the 1st hour. 

Sweat loss can range anywhere between 300 ml (about 10 fl oz) and 2.4 liters (2.5 quarts) per HOUR.  Although you will not replace fluids as fast as you will lose via sweat, it is important to try to hydrate enough so that you don’t lose more than about 2% of your starting body weight.  For a 135 lb person, he/she would not want to lose more than about 2.7 lb during exercise.  Measuring pre- and post- body weight will help you estimate how much fluid to replace during the next event to avoid losing more than 2% of your starting body weight. 

Without weight loss data, try this rule of thumb:  150 – 350 ml (6-12 fl oz) every 15 – 30 minutes, depending upon tolerance.

 

After Exercise

 

Carbs

After hard, intense, prolonged exercise, the muscle becomes a good “glycogen stuffer.”  The American Dietetic Association reports that muscle glycogen synthesis rate peaks with consumption of about 1.2 grams carbs/kg body weight/hour.  Wow!  That means a 135 lb (61.4 kg) person would consume about 74 grams carbs over the course of an hour during recovery.  That is equivalent to about 22 fl oz of Orange Juice – which incidentally, would also provide about 1260 mg of potassium – a much needed electrolyte to replenish after intense exercise. 

If you are curious, to consume 74 grams of carbs from original Gatorade, you’d have to consume 43 fl oz, and you would only get about 160 mg of potassium.  Although regular Gatorade is useful to consume while exercising since the concentration of carbs and electrolytes are easy to handle during high intensity exercise, it is not particularly efficient for recovery. 

 

Electrolytes

The more you sweat, the more fluid and electrolytes need to be replaced.  There are recovery products on the market, but you should experiment to find out what works for you.  Good recovery products will allow you to hydrate, replace electrolytes (sodium, potassium, and to a lesser extent, chloride, magnesium and calcium) and provide carbs for maximizing muscle glycogen synthesis.  If you don’t get electrolytes from recovery products, then you can simply get them from foods and drinks such as fruits, veggies, and naturally salty foods.  Unless a medical professional has told you otherwise, salt tablets and excessive use of the salt shaker is typically not necessary to replenish sodium – we get plenty in our foods.  For instance, vegetable soups (especially tomato) and vegetable juice contain a lot of sodium, chloride, and potassium. 

Incidentally, potatoes are particularly high in potassium (926 mg / medium baked potato weighing about 6 oz cooked).  A large banana provides about 487 mg potassium.  Nutrient values are from the USDA’s National Nutrient Database for Standard Reference. 

 

Water

According to the American Dietetic Association’s Position Statement on Nutrition for Athletic Performance, drink 16 – 24 fl oz of fluid for every pound of body weight loss during the activity or event.  As just a reminder, 8 fl oz = 1 cup.

 

Protein – Some General Comments

If you are trying to build or grow muscle, then be aware that adequate calories, protein, and muscle stimulus are necessary.  Generally, the increase in protein need to build muscle is not nearly as high as people assume.  As just an example, Benardot reports that Strength sports (including heavy weight training) require about 1.6 – 1.7 grams protein/kg body weight/day.  That is about double the RDA for the general population (0.8 grams/kg body weight/day), but it’s a lot less than what some protein supplement companies recommend.  I found one company that recommended 4 grams protein/kg body weight/day!  Endurance sports also require higher protein intake, but it’s closer to 1.2 – 1.4 grams/kg body weight/day, in the presence of adequate calorie intake. 

Conditions that more than double protein needs for adults are usually found in the hospital:  recovery from major burns, sepsis (systemic infection), and multiple major fractures.  It’s not body building!  If you are frustrated by lack of muscle development, then revisit your training regimen and calorie intake before you spend a lot of money on protein supplements. 

 

Good Nutrition – Basic Principles

Don’t forget that you are a human being first, an athlete/dancer second (although I know some argue otherwise).  For a review of healthy eating habits and estimated calorie need, see USDA’s MyPyramid.gov

 

Thanks for reading my blog!  If you have been placed on a modified diet by your physician or dietitian, then please follow that diet.  The information provided here is not intended to serve or replace medical advice.  I would love to read your comments, so please feel free to post!

Best –

Kathy Isacks, MPS, RD

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