Exercise Nutrition
1. Hydration and Fluid Intake in Athletes
Thermoregulation – the maintenance or regulation of temperature; specifically, the
maintenance of a particular temperature of the living body.
A loss of thermoregulation can result in hyperthermia (too hot) or hypothermia (too cold.)
Enzyme activity is also dependant on temperature. If there is an irregular temperature,
activity stops which means metabolic reactions stop.
The skeletal muscles produce 20-30 times more energy during exercise than at rest. Roughly
80% of this energy production forms heat and our core temperature can increase to 38-40
degrees. Therefore, we have to lose heat.
Mechanisms for heat loss include:
1. Radiation – electromagnetic heat waves are emitted are absorbed.
2. Convection – heat loss/gain through the movement of air/water.
3. Conduction – direct transfer of heat between molecules.
4. Evaporation – major method of heat loss, evaporation of sweat cools the skin and
each gram of sweat evaporated removes 2.4kj of energy.
These mechanisms are activated when the hypothalamus detects an increase in blood
temperature. This leads to an increase in cardiac output, blood flow redistribution through
vasodilation and constriction and the sweat glands absorb heat from the blood and move to
the surface.
The vapour pressure gradient – sweat draws heat away from the blood and is moved to the
skin surface as a liquid. For sweating to continue to happen it must be evaporated. The
speed at which this occurs depends on the vapour pressure gradient. A greater pressure
difference means more evaporation and a lower pressure difference is the opposite.
After exercising for a while, we start to lose fluid through sweat and if we don’t compensate
for these losses, we become dehydrated. Havong less bodily fluid available leads to an
increase in HR and it causes a decrease in heat loss.
Sweat Rate (L/hour) = Weight Loss + Volume Consume – Urine Loss / Duration of exercise.
A general assumption that a 2% loss of body water results in a 10% reduction
performance. This is because the elevated HR for thermoregulation limits the
amount of blood which can be sent to the active muscles.
Drinking Done Wrong: Hyponatremia
1. Excessive water intake during exercise dilutes sodium concentrations.
2. This leads to overhydration and an increase in body mass.
3. This causes exercise associated hyponatremia which is the dilution of plasma sodium
concentrations to under 135mmol/L.
, 4. There is then a water flux into the ICF and the severity of the symptoms related to
cell swelling depends on how much and fast plasma sodium decreases.
Those at the highest risk of hyponatremia are people with a lower body weight, females,
people exercising for over 4 hours, those that are exercising in cold temperatures and people
who use non-steroidal inflammatory agents.
Preventing Dehydration:
Before exercise – euhydration: 5-10ml/kg/BM 2-4 hours before exercise. Ensure urine is pale
yellow to clear and don’t drink too much. Considerations must be made for athletes that
have been in the heat for the previous few days.
During exercise – maintenance: this is highly individual and depends on the environment,
sweat rate and training status. Enough needs to be drunk to avoid losing 2% in BM.
After exercise – rehydration: 1.25 – 1.50L should be consumed for every 1Kg of BM lost to
account for continued water losses. Sodium intake can help retain water and alcohol should
be avoided because of its diuretic nature.
Osmolality – the concentration of dissolved particles in a fluid.
Fluid has to absorbed in the intestines. The speed at which this occurs depends on the
osmolality of the solution relative to the environment. An increase in the number of solutes
in fluid leads to an increase in osmolality.
Hypertonic solution – this can delay gastric emptying, result in exacerbating dehydration
and cause GI disturbances.
Hypotonic solutions – this helps maximise water uptake and it is the best for rapid
rehydration.
Isotonic solutions – this is optimal and generally seen in commercial sports drinks.
There are numerous reasons to include electrolytes in drink:
1. Sodium triggers a thirst response.
2. Higher volumes of sodium in the blood retain eater instead of losing it via the
kidneys.
3. It also replaces the electrolytes lost through sweating when exercising.
, 2. Protein Intake to Support Muscle Remodelling
Optimal protein needs can be measured through nitrogen balance and indicator amino acid
oxidation. Stable isotopes are used to measure protein synthesis on an acute (2-24hour)
level or a short-term (2-24 day) level.
Daily protein recommendation s vary from person to person. NBAL suggests 1.2-1.4g/kg/day.
For someone inactive, 0.8g/kg/day is recommended and for someone strength training, 1.6-
1.8g/kg/day is recommended.
Exercise stimulates both muscle protein synthesis and muscle protein breakdown, but in the
absence of food intake, net protein balance remains negative. Delaying protein intake by 1 or
3 hours after exercise had similar effects on muscle protein synthesis and net balance and
this is where that process was highest. Exercise also enhances anabolic sensitivity for several
hours up to several days.
20g of protein post exercise has been found to be an effective amount, however there are
factors such as different exercise types and body composition that could increase the
amount of protein needed.
The optimal daily protein distribution was found to be 20g every three hours as this induces
the greatest effects.
Does Type of Protein Matter?
Foods vary in AA composition and digestibility.
Protein quality is scored on the digestibility and quantity of essential AAs. This is
known as the Digestible Indispensable Amino Acid Score (DIAAS.)
Animal based protein typically score higher on protein quality than plant-based
protein.
Whey, milk and egg all have a high amount of EAA in them as well as leucine. The
likes of potato and corn are also relatively high in both.
Casein is also a good protein source. Despite it not being as rich in EAA, it has a much
slower digestion time therefore, leading to a more sustained elevation EAA and MPS.
Alternative Protein Sources:
Blending alternative
sources and the food
matrix can generate
similar results
compared to animal
products.
, 3. Energy and Athletic Performance
Energy balance is the balance between energy intake and energy expenditure. Therefore,
weight loss would require a greater amount of expenditure compared to intake and vice
versa for weight gain.
There is variability in how much energy a food product gives us, and this is dependent on
digestibility and its biochemical composition. On average, 1g of carbohydrates gives 4kcal, 1g
of protein gives 4kcal and 1g of fat gives 9kcal. There are also 7700kcal in 1kg of fat.
Roughly 70% of our energy expenditure throughout the day is a result of our Basal Metabolic
Rate, 10% is from the Thermic Effect of Food (eating,) another 10% is from Non-Exercise
Activity Thermogenesis and exercise makes up the rest of our energy expenditure.
Energy balance is important for athletes for weight management/body composition and
goals/periodisation. It also ensures that sufficient nutrients are taken on board for health
and performance.
Energy balance must be manipulated as often ‘competition weight’ can be dangerous and
unhealthy. Therefore, this needs to be periodised around competitions.
Manipulating Energy Intake:
Energy density – the amount of energy per gram of food. Lower density foods have lower
amounts of calories and vice versa. Low energy dense food tend to be high in water and
fibre and lower in fat. High energy dense food tend to be ultra-processed, higher in fat and
lower in water and fibre.
Food choices – athletes make food choices based on lifestyle, beliefs and knowledge,
psychological, social, economic, and physiological/biological reasons.
Food presentation – organising food on smaller plates or in a certain order can help to
manipulate food balance. The Delboeuf illusion is an example of this.
Macronutrients, appetite and satiety – protein appears to be the most satiating
macronutrient as it suppresses the appetite, causes diet-induced thermogenesis and it
invokes ghrelin stimulation.
1. Hydration and Fluid Intake in Athletes
Thermoregulation – the maintenance or regulation of temperature; specifically, the
maintenance of a particular temperature of the living body.
A loss of thermoregulation can result in hyperthermia (too hot) or hypothermia (too cold.)
Enzyme activity is also dependant on temperature. If there is an irregular temperature,
activity stops which means metabolic reactions stop.
The skeletal muscles produce 20-30 times more energy during exercise than at rest. Roughly
80% of this energy production forms heat and our core temperature can increase to 38-40
degrees. Therefore, we have to lose heat.
Mechanisms for heat loss include:
1. Radiation – electromagnetic heat waves are emitted are absorbed.
2. Convection – heat loss/gain through the movement of air/water.
3. Conduction – direct transfer of heat between molecules.
4. Evaporation – major method of heat loss, evaporation of sweat cools the skin and
each gram of sweat evaporated removes 2.4kj of energy.
These mechanisms are activated when the hypothalamus detects an increase in blood
temperature. This leads to an increase in cardiac output, blood flow redistribution through
vasodilation and constriction and the sweat glands absorb heat from the blood and move to
the surface.
The vapour pressure gradient – sweat draws heat away from the blood and is moved to the
skin surface as a liquid. For sweating to continue to happen it must be evaporated. The
speed at which this occurs depends on the vapour pressure gradient. A greater pressure
difference means more evaporation and a lower pressure difference is the opposite.
After exercising for a while, we start to lose fluid through sweat and if we don’t compensate
for these losses, we become dehydrated. Havong less bodily fluid available leads to an
increase in HR and it causes a decrease in heat loss.
Sweat Rate (L/hour) = Weight Loss + Volume Consume – Urine Loss / Duration of exercise.
A general assumption that a 2% loss of body water results in a 10% reduction
performance. This is because the elevated HR for thermoregulation limits the
amount of blood which can be sent to the active muscles.
Drinking Done Wrong: Hyponatremia
1. Excessive water intake during exercise dilutes sodium concentrations.
2. This leads to overhydration and an increase in body mass.
3. This causes exercise associated hyponatremia which is the dilution of plasma sodium
concentrations to under 135mmol/L.
, 4. There is then a water flux into the ICF and the severity of the symptoms related to
cell swelling depends on how much and fast plasma sodium decreases.
Those at the highest risk of hyponatremia are people with a lower body weight, females,
people exercising for over 4 hours, those that are exercising in cold temperatures and people
who use non-steroidal inflammatory agents.
Preventing Dehydration:
Before exercise – euhydration: 5-10ml/kg/BM 2-4 hours before exercise. Ensure urine is pale
yellow to clear and don’t drink too much. Considerations must be made for athletes that
have been in the heat for the previous few days.
During exercise – maintenance: this is highly individual and depends on the environment,
sweat rate and training status. Enough needs to be drunk to avoid losing 2% in BM.
After exercise – rehydration: 1.25 – 1.50L should be consumed for every 1Kg of BM lost to
account for continued water losses. Sodium intake can help retain water and alcohol should
be avoided because of its diuretic nature.
Osmolality – the concentration of dissolved particles in a fluid.
Fluid has to absorbed in the intestines. The speed at which this occurs depends on the
osmolality of the solution relative to the environment. An increase in the number of solutes
in fluid leads to an increase in osmolality.
Hypertonic solution – this can delay gastric emptying, result in exacerbating dehydration
and cause GI disturbances.
Hypotonic solutions – this helps maximise water uptake and it is the best for rapid
rehydration.
Isotonic solutions – this is optimal and generally seen in commercial sports drinks.
There are numerous reasons to include electrolytes in drink:
1. Sodium triggers a thirst response.
2. Higher volumes of sodium in the blood retain eater instead of losing it via the
kidneys.
3. It also replaces the electrolytes lost through sweating when exercising.
, 2. Protein Intake to Support Muscle Remodelling
Optimal protein needs can be measured through nitrogen balance and indicator amino acid
oxidation. Stable isotopes are used to measure protein synthesis on an acute (2-24hour)
level or a short-term (2-24 day) level.
Daily protein recommendation s vary from person to person. NBAL suggests 1.2-1.4g/kg/day.
For someone inactive, 0.8g/kg/day is recommended and for someone strength training, 1.6-
1.8g/kg/day is recommended.
Exercise stimulates both muscle protein synthesis and muscle protein breakdown, but in the
absence of food intake, net protein balance remains negative. Delaying protein intake by 1 or
3 hours after exercise had similar effects on muscle protein synthesis and net balance and
this is where that process was highest. Exercise also enhances anabolic sensitivity for several
hours up to several days.
20g of protein post exercise has been found to be an effective amount, however there are
factors such as different exercise types and body composition that could increase the
amount of protein needed.
The optimal daily protein distribution was found to be 20g every three hours as this induces
the greatest effects.
Does Type of Protein Matter?
Foods vary in AA composition and digestibility.
Protein quality is scored on the digestibility and quantity of essential AAs. This is
known as the Digestible Indispensable Amino Acid Score (DIAAS.)
Animal based protein typically score higher on protein quality than plant-based
protein.
Whey, milk and egg all have a high amount of EAA in them as well as leucine. The
likes of potato and corn are also relatively high in both.
Casein is also a good protein source. Despite it not being as rich in EAA, it has a much
slower digestion time therefore, leading to a more sustained elevation EAA and MPS.
Alternative Protein Sources:
Blending alternative
sources and the food
matrix can generate
similar results
compared to animal
products.
, 3. Energy and Athletic Performance
Energy balance is the balance between energy intake and energy expenditure. Therefore,
weight loss would require a greater amount of expenditure compared to intake and vice
versa for weight gain.
There is variability in how much energy a food product gives us, and this is dependent on
digestibility and its biochemical composition. On average, 1g of carbohydrates gives 4kcal, 1g
of protein gives 4kcal and 1g of fat gives 9kcal. There are also 7700kcal in 1kg of fat.
Roughly 70% of our energy expenditure throughout the day is a result of our Basal Metabolic
Rate, 10% is from the Thermic Effect of Food (eating,) another 10% is from Non-Exercise
Activity Thermogenesis and exercise makes up the rest of our energy expenditure.
Energy balance is important for athletes for weight management/body composition and
goals/periodisation. It also ensures that sufficient nutrients are taken on board for health
and performance.
Energy balance must be manipulated as often ‘competition weight’ can be dangerous and
unhealthy. Therefore, this needs to be periodised around competitions.
Manipulating Energy Intake:
Energy density – the amount of energy per gram of food. Lower density foods have lower
amounts of calories and vice versa. Low energy dense food tend to be high in water and
fibre and lower in fat. High energy dense food tend to be ultra-processed, higher in fat and
lower in water and fibre.
Food choices – athletes make food choices based on lifestyle, beliefs and knowledge,
psychological, social, economic, and physiological/biological reasons.
Food presentation – organising food on smaller plates or in a certain order can help to
manipulate food balance. The Delboeuf illusion is an example of this.
Macronutrients, appetite and satiety – protein appears to be the most satiating
macronutrient as it suppresses the appetite, causes diet-induced thermogenesis and it
invokes ghrelin stimulation.
