Additional Benefits of Caloric Restriction When Only Carbohydrate Calories Are Restricted

The Durk Pearson & Sandy Shaw®
Life Extension NewsTM
Volume 9 No. 4 • December 2006

Additional Benefits of Caloric Restriction
When Only Carbohydrate Calories Are Restricted

A new rat study of caloric restriction (CR) of late-middle-aged animals1 breaks new ground by using a diet in which fat calories and protein calories are the same in the restricted diet as for the ad libitum-fed rats; only carbohydrates (sucrose and cornstarch) are restricted. The beneficial results reported are very exciting because they point to an emphasis on a reduced-carbohydrate but high-protein (as a percentage of calories) diet for better long-term health.

In the usual CR diet, all sources of calories (carbohydrate, proteins, and fat) are restricted (vitamins and minerals are, however, fed at control levels), and, although CR has been shown to delay the onset of age-related mitochondrial abnormalities, it does not prevent the decline in ATP productivity needed to sustain muscle-protein fractional synthesis rate and contractile activity.1 The authors of this new study hypothesized that a limited ATP production during the usual CR is associated with a reduction in mitochondrial protein turnover and that maintaining protein intake during CR would stimulate mitochondrial protein turnover and improve mitochondrial protein oxidation and function. They looked at the effect of the carbohydrate-only CR (which we’re calling CarbCR) on the effect of mitochondrial function, as well as on muscle mass and function. The researchers looked at two types of muscle—soleus (a slow-twitch type) and tibialis anterior (a fast-twitch type)—because they exhibit different patterns of change with aging.

Increased ATP Production in CarbCR Rats

Carbohydrates in the CarbCR rats were restricted to about half of those consumed by the rats eating ad libitum, while fats and protein were the same as in the ad libitum diet. Wistar rats (21 months old) were fed either an ad libitum, 40% protein energy-restricted diet (which we’re calling AllCalCR for “all calories restricted,” the usual caloric restriction regimen) or a 40% CarbCR diet for 5 months. The weight loss observed in the CarbCR rats was the same as in the AllCalCR rats. However, there were no modifications of mitochondrial ATP production in either soleus or tibialis muscles in the AllCalCR group, whereas the CarbCR group had increased ATP production (by 30% in the soleus, P=0.07, and by 27% in the tibialis, P<0.05). Oxygen consumption in mitochondrial state 3 in the soleus decreased by 25% (P<0.05 vs. ad libitum) in the AllCalCR group but was maintained in the CarbCR rats.

In the tibialis, AllCalCR rats had the lowest mitochondrial-protein FSR (fractional synthesis rate) on synthesis of mitochondrial and myofibrillar proteins (e.g., myosin and actin, major contractile proteins) as compared to CarbCR and ad libitum. The reduction in muscle mitochondrial protein synthesis was significantly attenuated (P<0.05) in the CarbCR rats. Thus, maintaining protein intake significantly reduced the negative impact of an “all calories restricted” diet on muscle protein synthesis in the tibialis (a type II fiber).

Carbohydrate-Calorie-Restricted Rats Were Stronger

The authors report that absolute muscular force (grip force) was significantly increased in the CarbCR rats as compared with both the AllCalCR rats (7% greater, P<0.01) and ad libitum (18% greater, P<0.0001). The muscular force-to-body mass ratio was significantly increased in the AllCalCR rats (by 30%, P<0.0001, compared to ad libitum), but was increased even more in the CarbCR rats (by 49%, P<0.0001, compared to ad libitum and by 13%, P<0.01, compared to AllCalCR rats). The CarbCR rats exhibited a significant increase in the synthesis rates of myosin and actin, the major contractile proteins, as compared to the AllCalCR rats.

Reducing Carbohydrate Calories with a High-Fiber, High-Protein Whole Grain

One way to reduce carbohydrate calories while maintaining high protein levels is to substitute a high-fiber, high-protein, reduced-starch whole grain (such as our Glycemic Control™ line of extrahigh-beta-glucan, high-protein barley) in place of regular carbohydrates. The barley flour can be used in place of high-digestible-carbohydrate, lower-protein, and lower-fiber flours. The barley thick (not quick) flakes look like rice when cooked and have a nutty taste. We use them in cooked foods in place of rice. It makes a great barley pilaf, too—see recipe at the end of this newsletter. The barley quick flakes are great as a morning cereal, either with or without other cereals. Sandy mixes a little Go Lean Crunch®, a high-protein, high-fiber, low-sugar cereal (for extra crunch) along with 3 or 4 tablespoons of barley quick flakes for a snack or even a meal.

This study suggests that if you plan to reduce caloric intake or to select a different proportion of calorie sources in your diet, it is important to maintain your consumption of protein. Reduce carbohydrates, not protein. Eat fats in moderation, preferably monounsaturated and omega-3 polyunsaturated. Saturated fats should be eaten sparingly, as studies have shown, for example, that palmitic acid, a saturated fat found in fatty meats, butter, cream, etc., has negative effects on insulin sensitivity2 and promotes inflammation in adipose (fat) tissue.3 Moreover, another study4 reported that the ratio of oleic to palmitic acid content of the diet determines the thrombogenic (clot-promoting) and fibrinolytic (clot-busting) factors during the postprandial state in men. Increases in postprandial concentrations of tissue factor (prothrombotic) and plasminogen activator inhibitor-1 (antifibrinolytic), both of which increase the risk of clots, were observed when the ratio of oleic (monounsaturated fat) to palmitic acid (saturated fat) decreased. The same study also reports that n-3 LCPUFAs (DHA and EPA) may partially reduce the thrombotic potential of a fat-rich meal.


  1. Zangarelli et al. Synergistic effects of caloric restriction with maintained protein intake on skeletal muscle performance in 21 month old rats: a mitochondria-mediated pathway. FASEB J 20:2439-50 (2006).
  2. Solinas et al. Saturated fatty acids inhibit induction of insulin gene transcription by JNK-mediated phosphorylation of insulin-receptor substrates. Proc Natl Acad Sci USA 103(44):16454-9 (2006).
  3. Ajuwon and Spurlock. Palmitate activates the NF-kappaB transcription factor and induces IL-6 and TNFalpha expression in 3T3-L1 adipocytes. J Nutr 135:1841-6 (2005).
  4. Pacheco et al. Ratio of oleic to palmitic acid is a dietary determinant of thrombogenic and fibrinolytic factors during the postprandial state in men. Am J Clin Nutr 84:342-9 (2006).

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