Substrate Utilization

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• Metabolism is the sum of all chemical reactions with living cells to provide energy for vital processes.
• At rest, 33% of the body's energy comes from carbohydrates, or glycogen, stored within the muscles and liver. 66% comes from fat.
• During aerobic work, 50-60% of the energy comes from fats
  • Primarily carbohydrates are used during the first several minutes of exercise
  • For an average fit person, it takes 20 to 30 minutes of continuous aerobic activity to burn 50% fat and 50% carbohydrate
  • There is approximately a 7 fold increase of fat mobilization after 1 hour of exercise
• Proteins contribute less than 2% of the substrates used during exercise of less than 1 hour.
  • Slightly more proteins are utilized as a fuel source during prolonged exercise.
    • During the final moments of exercise lasting 3 to 5 hours, protein utilization may reach 5-15% of the fuel supply (Berg A & Keul J 1980; Cerretelli P 1977; Hood D & Terjung R 1990; Lemon P & Mullin F 1980; Lemon P & Nagle 1980)
  • Protein can supply up to 10% of total energy substrate utilization during prolonged intense exercise if glycogen stores and energy intake is inadequate (Brooks, 1987)
• The more fit an individual, the more they use fats over carbohydrates in the diet
  • Reaches steady state sooner, and stays there longer
  • Sympathetic stimulation mobilizes FFA
• On a low carbohydrate diet, you burn a higher proportion from fat
  • Endurance can be reduced up to 50% until body adapts
  • Adaptation to a low carbohydrate diet is possible if calories from protein and fat are sufficient
  • If calories are not sufficient, lean tissue (muscle) is utilized by gluconeogenesis (conversion of protein to glucose)
• Low intensity, high duration aerobics
  • Low intense exercise (<30% VO2 max) relies primarily on fat whereas high intense exercise (>70% VO2 max) primarily utilized carbohydrate.
  • Higher proportion of fat is expended (not necessarily more fat)
    • Lower intense submaximal exercise utilizes proportionally less carbohydrates
  • During low intense exercise prolonged exercise (ie greater than 30 minutes), a gradual shift from carbohydrate to fat metabolism occurs (Ball-Burnett MH, Green H & Houston M, 1991; Gollnick & Saltin B, 1988; Ladu M, Kapsas H & Palmer W, 1991; Powers S, Riley W, & Howley 1980)
• High intensity, low duration aerobics
  • More calories burned in less time
  • More carbohydrates, or glycogen utilized
    • Lactate threshold
      • Sedentary: 70-75% max heart rate
      • Trained: 80-90% max heart rate or higher
    • Intense or prolonged exercise can rapidly deplete muscle glycogen
  • Carbohydrates are used as a fuel source when more type II muscle fibers are recruited.
    • Type II muscle fibers have an abundance of glycolytic enzymes but few mitochondreal and lipolytic enzymes.
  • Increased blood levels of epiniphrine also increase the metabolism of carbohydrates.
    • High levels of epinephrine increase muscle glycogen breakdown, glycolysis and lactate production (Brooks G & Mercier J 1994).
  • Greater lactate production inhibits fat metabolism (Turcotte L, et al. 1995)
  • More fat metabolized hours intense exercise (Mulla, et al., 2000) (Phelain, et al., 1997)
• Weight training, plyometrics, sprinting, or high intense interval training
  • "It is known that the energy needs for sustaining maximal exercise of very short duration are largely met by the creatine phosphate breakdown such that its concentration decreases to almost zero at the end of maximal exercise leading to exhaustion. An almost complete creatine phosphate recovery is normally observed within rest periods lasting about 4 minutes following repeated maximal exercises of short duration." (Tremblay, et al., 1994)
  • Primarily carbohydrates utilized (after limited ATP and CP stores)
  • Fat is utilized many hours after anaerobic exercise
    • See weight training and HIIT studies

Glycogen

 

General Characteristics

• polysaccharide, (C-6, H-10, O-5)n
• stored primarily in the liver and muscle tissue
• readily converted to glucose as needed by the body to satisfy its energy needs
• supplies energy during heavy work.
• stored with water (1 gram of carbohydrates stored with 3 grams of water)
• central nevous system (CNS) is dependent on hepatic glycogen for energy

Glycogen and Performance

• Increased storage can double duration of exhaustive work
• Low or depleted glycogen stores
  • limits exercise intensity
  • decreases time to exhaustion
  • increases rating of perceived exhaustion during physical activity (Nieman, et al., 1987)
• The average person stores enough glycogen to last them 12 to 14 hours or over 2 hours with sustained moderate intensity.
  • Mean ingested daily is 400 grams
  • To maintain an adequate supply a minimum of 100 grams of carbohydrates should be ingested daily (Sources)
• Glycogen synthesis after exercise
  • Approximately 50% more glycogen can be stored if carbohydrates are consumed immediately following strenuous exercise as opposed to waiting 2 hours after exercise
    • Suggested amount
      • 100 g of carbohydrates (400 Kcal) for the average 175 lb man (Friedman et al 1991).
      • 10 – 20% of total daily caloric intake of carbohydrates and quality proteins in approximately a 4:1 ratio
  • Muscle glycogen synthesis is greater within 2 hours proceeding exercise (Friedman et al 1991) and greatest 45 minute post workout (Ivy JL 1988, Leven hagen DK 2001)
    • Exercise increases the muscle's sensitivity to insulin, predominately, during the 4 to 6 hours after exercise
    • During this time, muscle glycogen synthesis has been shown to be greater with ingestion of simple as compared with complex carbohydrates
    • After which, muscle glycogen can be resynthesized near pre-exercise levels within 24 hours, equivalently with either carbohydrates form
  • After 24 hours, muscle glycogen can increase very gradually, succeeding normal levels over the next few days (Ivy 1991).
• Super glycogen saturation technique can increase amount of work by 19%
  • Old method involved glycogen depletion through an initial low carbohydrate diet followed by a high carbohydrate diet
  • Newer method suggests glycogen depletion can be obtained by repeated prolonged intense exercise with similar results
  • Repeated muscle glycogen supercompensation is not possible, however performance enhancement is maintained (McInerney 2004)
  • Carbo-loading should not be done more than 3x/year
  • Preadolescent and adolescent individuals should not carbo-load

Carbohydrates

• Carbohydrates role

  • Fuel for activity
    • Immediate fuel for activity
    • Sustained energy for aerobic activity
    • Major energy for high intense activity like weight training or sprinting
  • Protein sparer - nervous system uses carbohydrates
    • Lack of carbohydrates causes protein to go through gluconeogenesis (conversion of protein to glucose) and be metabolized
  • Carbohydrates are metabolic primers, they are needed to completely burn fat
    • Incomplete combustion of fat will result in ketone bodies
    • Fat burns in the flame of carbohydrates.
  • Carbohydrates are the primary fuel for the CNS.
    • Accute carbohydrate depletion may cause tunnel vision, nausea, irritability
• Recomendations for athletes or physically active
  • 50%-60% of calories should be carbohydrates
    • 40%-50% from complex carbohydrates
    • 10% from simple sugar
  • Carbohydrate feedings during long duration (> 90 min.) submaximal (<70% VO2) can improve endurance performance (Coyle E & Montain S, 1992; Maughan R, 1991).
    • Carbohydrate ingestions of 30 to 60 grams per hour are required to improve performance
• Too little carbohydrates
  • More fat utilized as fuel source
  • Endurance can be reduced up to 50% until body adapts
  • Glycogen stores become depleted (Costill and Miller, 1980)
  • Ketosis: Break down of protein (muscle wasting) and incomplete combustion of fats (ketone bodies)
    • Possible symptoms: weakness, dizziness, tunnel vision, fatigue, panting, abnormal EEG, strange breath
    • Possible symptoms in diabetics: unconsciousness, coma and even possibly death in rare cases
    • Blood acidosis may impair exercise tolarance and performance.
  • Body can adapt and convert dietary protein to carbohydrates via gluconeogenesis
    • If low carbohydrate diet is coupled with insufficent dietary protein or calories
      • risk of burning lean tissue (muscle) by gluconeogenesis
• Too many carbohydrates
  • Converted to fat and stored
  • Increases body fat by suppressing fat oxidation
• Glycemic Index
  • High glycemic indexed food should be eaten with other foods
    • Soluble fiber, fat, acidic foods, and protein (particularly meat) significantly blunts insulin spike
    • Keep blood sugar stable
    • Inhibit hunger shortly after meal or snack

Protein

• Protein is used for building, maintaining and repairing muscle, skin, blood, and other tissues

  • energy takes priority over tissue building
• Very little protein is used as fuel when caloric supply is adequate
  • The best fuel choices are carbohydrates and fats
  • If carbohydrates are not adequate, protein can convert to carbohydrates via gluconeogenesis
  • Nitrogen excretion does not rise following physical activity when carbohydrates are adequate.
    • Protein contains nitrogen
• The best sources of protein
  • Eggs, milk, and meat
  • Certain vegetable proteins can be eaten together or with animal proteins to compliment proteins for proper amino-acid ratios
    • Beans
      • High in lysine, low in methionine
      • Soybean are the exception
    • Grains
      • High in methionine, low in lysine
         

        Complimentary Proteins (add one from each list)
        Kidney Beans White Beans Lima Beans Lentils Chick Peas Green Peas Black-eyed Peas Peanuts	Bread Pasta Rice Bulgur Couscous Corn Almonds Sesame Seeds

• Average consumption for U.S. is 100 grams/day
• Protein requirements
  • 10% to 20% of the diet should be protein for sedentary individuals
    • 40 grams/day for females
    • 55-70 grams/day or 0.8 grams/kg body weight for males
  • Recommended protein intake for athletes or physically active people (Paul 1989)
    • Protein and carbohydrate requirements increase somewhat
      • more calories
      • ratio of protein to carbohydrates does not change
    • 12% to 20% of the total calories
    • Increases slightly during an increase or change of training
    • Surprisingly greater protein requirements for endurance athletes than weight trained athletes
  • Protein requirements increase when calories are insufficient

Athletes and Physically Active Individuals

It has been shown that the protein requirements for athletes may well exceed that suggested by the (USRDA) .80 g/kg/day. If an individuals protein requirement increases in response to exercise, then changes in protein metabolism will become apparent. When the body is in a homeostatic state, protein synthesis is equal to protein degradation and the protein requirement of the body for tissue maintenance is satisfied. The most common way to detect changes in protein metabolism is to assess nitrogen balance of the body.

Positive nitrogen balance occurs when the total nitrogen excreted in the urine, feces and sweat is less than the total nitrogen ingested. Positive nitrogen balance must exist for new tissue to be synthesized. When dietary protein intake or total energy intake is inadequate to maintain tissues total nitrogen balance, negative nitrogen balance occurs and new tissue is unable to be synthesized. When the body is in nitrogen balance, protein and energy intake is sufficient to maintain tissue protein needs and the amounts of nitrogen entering and exiting the body are equal.

The results of nitrogen balance studies on endurance athletes indicates that these athletes have protein requirements that exceed the USRDA of 0.8 g/kg/day. A study found that endurance athletes (defined as training for at least 12 hours per week for at least 5 years) require 1.37 g/kg/day of protein to maintain nitrogen balance compared to 0.73 g/kg/day for sedentary individuals.

It appears that weight training can also lead to a daily protein requirement that exceeds the current USRDA. It has been found that 2.0 to 2.2 g/kg/day of protein was barely sufficient to maintain nitrogen balance during moderate intensity weight training. Furthermore, weightlifter's protein requirements increased proportionally to training intensity. Research has shown that 2.0 to 2.6 g/kg/day of protein are required for periods of very intense weight training, whereas protein intakes of 2.0 g/kg/day maintained a positive nitrogen balance during periods of less intense weight training.

It is clear that athletes need to consume more protein than the current USRDA for 0.8 g/kg/day in order to maintain nitrogen balance. Conversely, since the requirements of carbohydrates, and overall calories also increase with physical activity, the recommended proportion of calories from protein does not change significantly. With a calorie sufficient diet, protein requirement values needed to maintain positive nitrogen balance of both weight trained and endurance trained athletes constitutes intakes of 12% to 20% of total daily calories.

Paul GL. Dietary protein requirements of physically active individuals. Sports Med 1989; 8:154-176.

Weight Loss

Obese individuals eating a slightly higher protein diet (25% of calories from protein), lost significantly more weight and body fat than those eating a slightly lower protein diet (12% of calories from protein). (Skov, et. al., 1999)

Overweight women consuming a diet with a carbohydrate/protein ratio of 1.4 (125 g protein/day) lost more weight and body fat than those eating a ratio of 3.5 (68 g protein/day).

Layman DK, Boileau RA, Erickson DJ, Painter JE, Shiue H, Sather C, Christou DD. (2003) A reduced ratio of dietary carbohydrate to protein improves body composition and blood lipid profiles during weight loss in adult women. J Nutr. 133(2):411-7.

Skov AR, Toubro S, Ronn B, Holm L, Astrup A (1999). Randomized trial on protein vs carbohydrate in ad libitum fat reduced diet for the treatment of obesity. Int J Obes Relat Metab Disord. 23(5):528-36.

Fat

• Weight management

  • Dietary fats are stored and mobilized easily
    • It takes more energy for the body to convert carbohydrates or protein to body fat than it does to convert dietary fat to body fat
      • see thermic effect of food
  • Typically, less calories are consumed when eating a low fat diet (Lissner 1987, Thomas 1992).
  • A reduction in dietary fat without a reduction in total calories or an increase of physical activity only produces small if any changes in body fat mass (Leibel 1992).
• High fat diets may limit endurance if carbohydrates are low and body is accustome to a higher carbohydrate diet.
  • A high fat diet may actually increase endurance in certain elite athletes particularly if they have adapted to such a diet
  • There is no net glucose synthesis from lipids except from glycerol portion - 10% by weight
• Polyunsaturated and monounsaturated fats are preferred in the diet
  • Found in fish, nuts, vegetable oils
    • Contain essential fatty acids which help to reduce cholesterol deposits
    • Omega 3 fatty acids
      • 2 serving (8 oz) of fish (low mercury) per week recommended
  • Saturated fats can be converted to cholesterol or LDL
    • See Saturated fats and additional fat exchages
  • Trans-unsaturated fat may act like saturated fat, eg: margarine, hydrogenated oil.
    • Processed foods and oils provide 80% of trans fats in diet
    • Animal sources only provide 20% of trans fats (naturally occurring) in diet
• American Dietary Guidelines (2005)
  • A high fat intake (greater than 35% of calories)
    • associated with higher saturated fat intake
      • keep saturated fat below 10% of calories
    • more difficult to avoid consuming excessive calories
  • Low fat intake (less than 20% of calories)
    • increased risk of inadequate intakes of vitamin E and essential fatty acids
    • may contribute to unfavorable changes in HDL and triglycerides

Food Exchanges

Food Exchange	US Unit	Metric	Comments
Starches	80 Calories		15 g Carb., 3 g Protein, 1 g Fat
bread breads, other tortilla crackers cooked cereals dry cereals, unsweetened dry cereals, sweetened dry flour or grain pasta rice corn popcorn potato (small) potato, mashed sweet potato squash, winter cooked beans, peas, lentils (add 1 meat exchange)	1 slice 1 oz 1 (6") 4-6 (3/4 oz) 1/2 cup 3/4 cup 1/2 cup 3 Tbsp 1/2 cup 1/3 cup 1/2 cup 3 cups 1 (3 oz) 1/2 cup 1/3 cup 1 cup 1/2 cup	1 slice 30 g 1 (15 cm) 4-6 (20 g) 125 ml 175 ml 125 ml 45 ml 125 ml 80 ml 125 ml 720 ml 1 (85 g) 125 ml 80 ml 250 ml 125 ml	Most starches are a good source of B vitamins Choose whole grain foods such as 100% whole wheat bread, pasta, tortillas, and brown rice, etc. for nutrients and fiber. Combine beans (starch & meat) with grains (starch) for their complimentary proteins and fiber Combine grains (starch) with milk (milk) or cheese (meat) to compliment proteins. Add additional fat exchanges for starchy foods prepared with fat.
Vegetables	25 Calories		5 g Carb., 2 g Protein
raw vegetables cooked vegetables tomato or vegetable juice	1 cup 1/2 cup 1/2 cup	250 ml 125 ml 125 ml	Choose more dark green leafy and deep yellow vegetables such as spinach, broccoli, carrots, and peppers.
Fruit	60 Calories		15 g Carb.
fresh fruit melon (cubes) canned fruit dried fruit fruit juice	1 small 12 oz (1 cup) 1/2 cup 1/4 cup 1/2 cup	1 small 360 g (250 ml) 125 ml 60 ml 125 ml	Choose whole fruits for fiber Choose citrus fruits such as oranges, grapefruits, or tangerines
Meat & Substitutes	35-145 Calories		7 g Protein, 0-13 g Fat
meat, poultry, fish cheese cottage cheese egg peanut butter tofu cooked beans, peas, lentils (add 1 starch)	1 oz 1 oz 1/4 cup 1 1.5 Tbsp 4 oz (1/2 cup) 1/2 cup	30 g 30 g 60 ml 1 22 ml 115 g (125 ml) 125 ml	Choose leaner meats such as chicken, fish, and lean cuts of meat; add fat exchange for higher fat meats and substitutes. Remove skin from poultry. Limit frying or adding fat. Have 2 servings of fish per week for Omega 3 fatty acid.
Milk	80-150 Calories		12 g Carb., 8 g Protein, 0-8 g Fat
milk yogurt	1 cup 1 cup	250 ml 250 ml	Choose lower fat milks; add fat exchange for higher fat milk.
Fat	45 Calories		5 g Fat
oil mayonnaise cream cheese salad dressing peanuts avocado butter or margarine higher fat exchange (additional)	1 tsp 1 tsp 1 Tbsp 1 Tbsp 10 1/8 1 tsp 1 exchange	5 ml 5 ml 15 ml 15 ml 10 1/8 5 ml 1 exchange	Eat less saturated fat such as animal fat found in fatter meat, cheese, and butter. Also eat less hydrogenated fat and trans-fatty acids. Consume mono-unsaturated and poly-unsaturated fat Check Nutrition Facts on food labels; 5 g Fat = 1 Fat exchange.
Sweets	Calories vary		15 g Carb., Protein & Fat varies
ice cream cookies syrup jam or jelly sugar pudding muffin or cupcake	1/2 cup 2 small 1 Tbsp 1 Tbsp 2 Tbsp 1/4 cup 1/2 small	125 ml 2 small 15 ml 15 ml 30 ml 60 ml 1/2 small	Choose sweets sparingly because they are high in fat or sugar. Can be substituted for a 1 Starch, Fruit, or Milk exchange. Add 1 or 2 Fat exchanges for sweets containing fat.