Skip to main content Accessibility help
×
Home

Contents:

Information:

  • Access

Actions:

      • Send article to Kindle

        To send this article to your Kindle, first ensure no-reply@cambridge.org is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about sending to your Kindle. Find out more about sending to your Kindle.

        Note you can select to send to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.

        Find out more about the Kindle Personal Document Service.

        Casein limits the loss of fat-free mass during food restriction in obese rats
        Available formats
        ×

        Send article to Dropbox

        To send this article to your Dropbox account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your <service> account. Find out more about sending content to Dropbox.

        Casein limits the loss of fat-free mass during food restriction in obese rats
        Available formats
        ×

        Send article to Google Drive

        To send this article to your Google Drive account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your <service> account. Find out more about sending content to Google Drive.

        Casein limits the loss of fat-free mass during food restriction in obese rats
        Available formats
        ×
Export citation

Treatment of obese patients with restrictive diets induces not only a loss of fat mass but also of fat-free mass( 1 ). A sufficient amount of protein in the diet is necessary to limit this loss, but for the same level of protein, the kinetics of amino acid delivery to the organism could play a role( 2 , 3 ). The objective of the present study was to limit food restriction-induced loss of fat-free mass by varying the nature of ingested proteins. Casein (slowly digested), milk soluble proteins (MSP; rapidly digested), and a mixture of casein–MSP (50/50, w/w) were tested.

Obesity was induced in four groups of male Wistar rats weighing 324.3 (se 9.9) g by feeding them ad libitum for 5 weeks with a semi-liquid diet containing (% energy) 14 protein (PR), 40 carbohydrates (CHO) and 45 lipids (LIP). One of these groups was killed (obese rats, n 9) and the three other groups were then fed a restricted amount of a diet containing casein (n 19), MSP (n 18) or the casein–MSP mixture (n 18) as the only source of protein for 3 weeks (% energy; 37 PR, 35 CHO and 28 LIP). A control group (n 10) was fed a diet with (% energy) 19 PR, 69 CHO and 10 LIP ad libitum for 5 weeks. Weight and food intake were recorded. In vivo fractional protein synthesis rates (FSR) were measured in extensor digitorum longus muscle in the fed state using the flooding-dose method and [1-13C]valine as the tracer. Body composition was measured in restricted rats by dual-energy X-ray absorptiometry at the beginning and at the end of the restricted diet. Rats were killed and tissue weights were measured (hind-limb muscles, kidney, intestine, liver, spleen).

Only body weight (+8%; P<0.01) and peri-renal (+41%; P<0.05) and peri-genital (+28%; P<0.05) fat masses were significantly increased in obese rats compared with controls. Muscle FSR were unchanged. During food restriction, intake was similar for casein-, MSP- or mixture-fed rats and averaged 45% energy intake of control rats. The lower energy intake induced a significant decrease in weight (−12%; P<0.01), fat mass (−39%; P<0.01) and muscle FSR (−26%; P<0.01). Casein-fed rats maintained a higher weight (+7%; P<0.01), fat-free mass (+6%; P<0.005), liver weight (+10%; P<0.01) and intestine weight (+18%; P<0.01) than MSP- or mixture-fed rats, while only their muscle weight tended to be higher (P=0.06). Muscle FSR (%/d) were not different between rats fed casein (3.8 (se 0.1)), MSP (4.4 (se 0.3)) or mixture (3.3 (se 1.0)) diet (but it was higher in MSP-fed rats than in mixture-fed rats).

Casein allows a sparing of fat-free mass during food restriction in obese rats. This result is not explained by a higher muscle FSR in the fed state, but it could result from: (a) the maintenance of a high muscle FSR for a longer period of time; (b) a higher muscle FSR in the post-absorptive state; (c) a greater inhibition of muscle protein degradation. Further studies are necessary to answer these questions.

1. Chaston, TB, Dixon, JB & O'Brien, PE (2007) Int J Obes (Lond) 31, 743750.

2. Boirie, Y, Dangin, M, Gachon, P, Vasson, MP, Maubois, JL & Beaufrère, B (1997) Proc Natl Acad Sci U S A 94, 1493014935.

3. Lacroix, M, Bos, C, Léonil, J et al. . (2006) Am J Clin Nutr 84, 10701079.