Metabolic Expression and Exercise | Exercise Intensity and Nutrient Need

Apr 30 , 2021


Fluid Fitness

Metabolic Expression and Exercise | Exercise Intensity and Nutrient Need

There are metabolic differences between sedentary and trained individuals; therefore, it is important to know where you fall and feed your goals accordingly.




Energy Needs & Metabolic Changes with Exercise

The amount of energy that is expended in physical activity can fluctuate with intensity, duration, type of exercise and body weight. However, we do know that no matter the exercise there are metabolic changes that happen when a person goes from a sedentary lifestyle to participating in regular physical activity. During low levels of or submaximal sustained exercise (ex: walking), fat oxidation (burning fat for energy) plays a more important role. As physical activity intensifies the role of fat oxidation decreases and the role of carbohydrate (or glycogen stores) as the energy source increases. In light-moderate aerobic exercise (ex: jogging), the use of stored fat as energy decreases to 50-60%. With intense exercise (ex: sprinting, racing or other intense activity) the body will rely primarily on glycogen stores (i.e., carbohydrates) for energy. The balance energy source and therefore intake favors fat for more sustained lower intensity exercise and carbohydrates for shorter more intense exercise (always keeping at least a minimum intake of 40% carbohydrates and 25% fat. Also note that biochemical changes that occur with consistent training increase the amount of glycogen that can be stored in the muscles by approximately 20-50%.




Nutrient Specific Needs

- Carbohydrates: Inadequate carbohydrate intake can potentially hurt training and performance and increase the likelihood of experiencing cravings and unwanted hunger, especially later in the day. For an individual participating in moderate exercise (about 1 hour/day) the general recommendation is 4-6 grams of carbohydrates per kg body weight. For an endurance athlete training 1-3 hours per day, the carbohydrate needs increase to 5-9 grams per kg body weight. Whole food sources of carbohydrates is also preferable, making sure that over half, if not all are complex carbohydrates. These sources have higher amounts of fiber and other nutrients that are essential, especially with increased exercise intensity.


- Fat: Because fat oxidation is so important in low to moderate exercise, adequate intake from healthy fat sources is essential. The minimum amount of fat intake for an individual participating in low to moderate exercise (about 1 hour per day) is 25%. Depending on the activity and duration the fat recommendation can increase. In general, most consistently active individuals should have about 30% of the calories coming from fat. Daily fat intake should be focused on unsaturated fats (both mono and poly), with limited saturated fat intake and complete avoidance of Trans fats. These healthier sources will help make sure the body is getting enough essential fatty acids that are important in a number of systems including inflammation regulation.


- Protein: Although protein is not the bodies preferred source of energy, in endurance or other intense exercise, about 5% of energy usage can come from protein. Especially if glycogen store are depleted and blood glucose is low. Even more important however, is that adequate protein intake is essential for the building and repairing of muscles and other tissues. The minimum amount of protein for a sedentary individual is 0.8 grams per kg body weight. This minimum increases with physical activity to 1.1-1.6 g/kg for recreational exercisers and 1.3 to 1.6 for endurance athletes. An active adult trying to build muscle mass will often need even more protein: 1.6-1.8 g/kg body weight. It is also important to note that an untrained individual starting up on an exercise program often requires extra protein to help begin building muscle mass.


- Fluid & Electrolytes: Fluid needs vary from person to person, however there are ways to calculate average needs (ex: ½ body weight in ounces). All of the popular ways to calculate fluid needs only account for the base of what an individual needs and does not take into account exercise. Sweat rates commonly range between 1-4 pounds per hour, depending on the sport, body size, intensity, clothing, weather, etc. The goal is to strive for water balance before beginning exercise; drink 2-3ml of water per pound body weight at least 4 hours before exercise. Have a water bottle handy during exercise and make sure to continue to replenish post-exercise. Many minerals such as sodium (~800mg/2lb sweat), potassium (~200mg/2lb sweat), calcium (~20mg/2lb sweat) and magnesium (~10mg/2lb sweat) are also lost during exercise through sweat. These minerals can be replenished through food consumed before and after workouts and even throughout the day with other meals. Generally, sports or other electrolyte enhanced drinks are not needed unless and individual is participating in intense continuous exercise for longer than an hour at a time.


Bringing it All Together

Energy is the human body’s primary dietary requirement. Inadequate energy intake can result in protein, vitamins, minerals and other nutrients not being used effectively for their metabolic functions. Adequate energy and nutrient intake is important for optimal exercise performance and recovery. Consuming too few calories or an inadequate balance of nutrients can cause damage in the body and create disruption in many systems. For example, consuming too few calories can cause more protein (instead of carbohydrates or fat) to be converted to glucose and burned as energy instead of being used to build and repair muscles. For better nutrient balance, consume at least 3, preferable 4 different kinds of nutrient dense foods at each meal. The more types of foods consumed results in more and a greater variety of vitamins, minerals and other nutrients taken in.



Be Aware:

 As in previous weeks, being aware is always the first step to making changes. Review this week’s presentation and write-up. Review the information provided to identify where you fall in increased needs with exercise. Take note of what is recommended for an individual that most closely matches your own activity level.

Take Note: Continue your food journal from previous weeks. Complete for at least 3-4 days, but is best if you can complete for an entire week. Either input your intake into a tracking application or complete the calculations yourself to see what your average consumption is for calories, carbohydrates, protein and fat. See how this compares to what the recommendations are for someone at your activity level.

Take Action:

- Alter: if you note a mismatch in your intake versus your needs, try making an adjustment. Add or remove certain foods to try to correct the imbalance.

- Consult: If you are having trouble identifying patterns, calculating your specific needs, picking out culprits of dietary imbalance or just want more guidance in your diet plan, consult a registered dietitian.


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