Written by Layne Norton
03 November 2011

By Layne Norton

“Young men think old men are fools; but old men know young men are fools.”

            —George Chapman (1559-1634)

 Much has been written about nutrition in the pages of MD over the decades. I’m sure many readers who began reading when they were teenagers are now entering their 30s and 40s. Countless pages have been devoted to describing nutritional protocols to maximize gaining muscle and losing fat. But I submit to you that we have all been fools— not just the young as George Chapman implies. There are fundamental metabolic differences between age groups— yet most nutritional recommendations for maximizing muscle don’t take age into account! In this young fool’s opinion, it’s time we all examined optimal anabolic eating for YOUR age, addressing each of the macronutrients.

Protein

We might as well get the big issue of protein intake out of the way first. If you read MD, you know high-protein meals increase muscle protein synthesis and this builds more muscle. The question is, how does age affect this anabolic response to protein? Research suggests that younger individuals are very sensitive to the anabolic effects of amino acids.1-3 However, as we age, we become less sensitive to the anabolic effects of amino acids. Several researchers have shown that comparatively large doses of amino acids are required to maximize the anabolic response in the elderly, as opposed to the young subjects.1,2,5-9

It appears the decreased response in the elderly may be explained by a decrease in the muscle cell content and activity of mTOR and p70S6K, two kinases involved in directing protein synthesis.2,5 According to this research, older subjects require a greater amount of amino acids, specifically leucine (the amino acid responsible for stimulating protein synthesis), to maximize protein synthesis, as opposed to younger subjects.7-9 Furthermore, it appears that the decreased anabolic response in the elderly may be due, at least in part, to increased production of reactive oxygen species (ROS) with age.

ROS has been shown to decrease mTOR activity and inhibit protein synthesis.10 But there is hope— it has been demonstrated that supplementation with a combination of antioxidants (rutin, vitamin E, vitamin A, zinc and selenium) restores the anabolic effect of a meal to the same level as the young!11 So make sure you eat plenty of protein that is high in leucine (e.g., whey) and keep room in that pillbox of yours for some antioxidants, Grandpa!

Protein Recommendations:

<20 years old: 0.7-1 grams/pound bodyweight

21-40 years old: 0.9-1.2 grams/pound bodyweight

41-65 years old: 1.1-1.4 grams/pound bodyweight

>65 years old: 1.3-1.5 grams/pound bodyweight

 

Carbohydrates

Carbohydrates are another macronutrient that differentially impact anabolism as people age. The primary way in which carbohydrates influence anabolism is by increasing insulin secretion. Young individuals are very sensitive to the anabolic effects of insulin and in their case, carbohydrates alone may be sufficient to increase protein synthesis and also inhibit protein degradation.12 Recall that Net Muscle Gain = Muscle Protein Synthesis - Muscle Protein Degradation, so insulin is both anabolic and anti-catabolic in young individuals.

In adult subjects, carbohydrates fail to increase protein synthesis when they are consumed alone.13 Carbohydrates do have a synergistic effect on protein synthesis with amino acids in adults and can induce a greater anabolic response when combined with protein, as opposed to consuming protein alone.14 It also appears that insulin will still inhibit protein degradation in adults and therefore is anti-catabolic, with the potential to optimize the anabolic effects of amino acids.15

Though little data is available for the elderly, it is clear that physiological increases in insulin that would be induced by consuming carbohydrates alone will not stimulate muscle protein synthesis.14 It does appear that, in the elderly, co-ingestion of carbohydrates with amino acids does provide a small anabolic advantage over amino acids alone.14 Since carbohydrates do not provide the same anabolic advantage to the elderly as they do other age groups and because aging reduces insulin sensitivity, it is likely that elderly muscleheads will want to consume less carbohydrates than young or adult individuals.16

Carbohydrate Recommendations:

<20 years old: 2.2-3.2 grams/pound bodyweight

21-40 years old: 1.7-2.7 grams/pound bodyweight

41-65 years old: 1.2-2.2 grams/pound bodyweight

>65 years old: 0.7-1.7 grams/pound bodyweight

Keep in mind, these recommendations are for maximizing muscle gain and will need to be adjusted accordingly for individuals wanting to lose body fat.

 Fat

 The difference in how dietary fat should be consumed as one ages should largely be influenced by the changes in carbohydrate intake with age. As outlined previously, one should gradually reduce carbohydrate intake throughout their life as they age. Therefore, someone who is younger and still sensitive to the anabolic effects of carbohydrates will be better off consuming lower fat with more carbohydrates, while an elderly individual will want to consume far less carbohydrates and fill in those calories instead with more protein and fat.

            Fat is a very important macronutrient and it’s important that one never let it fall too low. I recommend that fat intake never be less than 0.2 grams per pound of bodyweight. Even if the individual is young and highly sensitive to the anabolic effects of insulin, it’s still important to consume sufficient fat.

Fat Recommendations:

<20 years old: 0.25-0.4 grams/pound bodyweight

21-40 years old: 0.35-0.5 grams/pound bodyweight

41-65 years old: 0.45-0.6 grams/pound bodyweight

>65 years old: 0.55-0.7 grams/pound bodyweight

Keep in mind that these are just general recommendations. Optimal macronutrient intake is based on numerous factors and it is always best to experiment to find out what will fit best with your individual metabolism. This article will help everyone better understand how age can impact optimal macronutrient profiles and the adjustments that can be made to best optimize these macronutrient profiles.

References:

1. Paddon-Jones D, Sheffield-Moore M, Zhang XJ, Volpi E, Wolf SE, Aarsland A, Ferrando AA, Wolfe RR. Amino acid ingestion improves muscle protein synthesis in the young and elderly. Am J Physiol Endocrinol Metab, 2004 Mar;286(3):E321-8.

2. Cuthbertson D, Smith K, Babraj J, Leese G, Waddell T, Atherton P, Wackerhage H, Taylor PM, Rennie MJ. Anabolic signaling deficits underlie amino acid resistance of wasting, aging muscle. FASEB J, 2005 Mar;19(3):422-4.

3. Drummond MJ, Miyazaki M, Dreyer HC, Pennings B, Dhanani S, Volpi E, Esser KA, Rasmussen BB. Expression of growth-related genes in young and old human skeletal muscle following an acute stimulation of protein synthesis. J Appl Physiol, 2008 Sep 11. [Epub ahead of print]

4. Welle S, Thornton CA. High-protein meals do not enhance myofibrillar synthesis after resistance exercise in 62- to 75-yr-old men and women. Am J Physiol, 1998; 274 (4 Pt 1):E677-E683.

5. Guillet C, Prod’homme M, Balage M, et al. Impaired anabolic response of muscle protein synthesis is associated with S6K1 dysregulation in elderly humans. FASEB J, 2004; 18:1586-1587.

6. Katsanos CS, Kobayashi H, Sheffield-Moore M, et al. Aging is associated with diminished accretion of muscle proteins after the ingestion of a small bolus of       essential amino acids. Am J Clin Nutr, 2005; 82:1065-1073.

7. Katsanos CS, Kobayashi H, Sheffield-Moore M, et al. A high proportion of leucine is required for optimal stimulation of the rate of muscle protein synthesis by essential amino acids in the elderly. Am J Physiol Endocrinol Metab, 2006; 291:E381-E387.

8. Dardevet D, Sornet C, Bayle G, et al. Postprandial stimulation of muscle protein synthesis in old rats can be restored by a leucine-supplemented meal. J Nutr, 2002; 132:95-100.

9. Rieu I, Balage M, Sornet C, et al. Increased availability of leucine with leucine-rich whey proteins improves postprandial muscle protein synthesis in aging rats. Nutrition, 2007; 23:323-331.

10. Patel J, McLeod LE, Vries RG, Flynn A, Wang X, Proud CG. Cellular stresses profoundly inhibit protein synthesis and modulate the states of phosphorylation of multiple translation factors. Eur J Biochem, 2002 Jun;269(12):3076-85.

11. Marzani B, Balage M, Vénien A, Astruc T, Papet I, Dardevet D, Mosoni L. Antioxidant supplementation restores defective leucine stimulation of protein synthesis in skeletal muscle from old rats. J Nutr, 2008 Nov;138(11):2205-11.

12. Fujita S, Rasmussen BB, Cadenas JG, Grady JJ, Volpi E. Effect of insulin on human skeletal muscle protein synthesis is modulated by insulin-induced changes in muscle blood flow and amino acid availability. Am J Physiol Endocrinol Metab, 2006 Oct;291(4):E745-54.

13. Gautsch TA, Anthony JC, Kimball SR, Paul GL, Layman DK, Jefferson LS. Availability of eIF4E regulates skeletal muscle protein synthesis during recovery from exercise. Am J Physiol, 1998 Feb;274(2 Pt 1):C406-14.

14. Volpi E, Mittendorfer B, Rasmussen BB, Wolfe RR. The response of muscle protein anabolism to combined hyperaminoacidemia and glucose-induced hyperinsulinemia is impaired in the elderly. J Clin Endocrinol Metab, 2000 Dec;85(12):4481-90.

15. Rasmussen BB, Fujita S, Wolfe RR, Mittendorfer B, Roy M, Rowe VL, Volpi E. Insulin resistance of muscle protein metabolism in aging. FASEB J, 2006; 20:768-769.

16. Kruszynska YT, Petranyi G, Alberti KG. Decreased insulin sensitivity and muscle enzyme activity in elderly subjects. Eur J Clin Invest, 1988 Oct;18(5):493-8.