VoedingsMagazine - nummer 4, december 2011, 24e jaargang
NutritionMagazine, No.4, 2011, Vol.24
Conclusion from the Canadian IDEAL study
Consumption of dairy products promotes a gain in fat-free mass during slimming
In the IDEAL (Improving Diet, Exercise And Lifestyle) study overweight and obese women followed for 16 weeks energy-restricted diets varying in share of dairy products and protein content. The diet with the highest level of dairy consumption and a high protein level resulted in the highest loss of body fat and an increase in fat-free boy mass. The researchers concluded that a high protein intake, notably protein from dairy products, combined with energy restriction and anaerobic and resistance training can contribute appreciably to improved body composition during a period of weight loss.
It is beyond dispute that weight loss can yield considerable health benefits for people with overweight or obesity. However, it is essential that during a period of weigh loss in particular adipose tissue is lost and that fat-free mass is spared as far as possible. The composition of the diet followed during slimming can affect the changing balance between body fat and fat-free mass. A recent publication in Journal of Nutrition shows that a diet high in dairy products as an element of an energy-restricted diet results in a more favourable body composition (1, 2). The first author of the paper is Andrea Joss, a graduate student in the Exercise Metabolism Research Group of Prof. Stuart Phillips (McMaster University, Hamilton, Ontario, Canada). Study participants were 90 overweight and obese women aged 19—45 with a BMI of 27—40 kg/m2. Other inclusion criteria were a sedentary lifestyle and a low habitual consumption of dairy products (accounting for less than 20% of total energy intake, corresponding with less than one dairy serving a day on average; a serving of dairy products was defined in the IDEAL study as 250 ml milk, 50 g cheese or 175 ml yoghurt).
Protein intake up to 30% of total energy intake The participants were randomized into three groups of women who participated in a training programme and followed an energy-restricted diet for 16 weeks. The training programme (aerobic and resistance training) was followed on five days per week in the university's sports facilities. The participants were requested to train on themselves in the weekends. Mean energy expenditure per training session was 1 MJ. Daily dietary energy intake was 2 MJ lower than daily energy expenditure. The diets of the three groups varied in protein content and in quantity of dairy products consumed per day. Participants in the adequate-protein/low-dairy (APLD) group upheld their habitual low consumption of dairy products and were instructed to follow a diet with 15% protein (as a proportion of total energy intake). Women in the adequate-protein/medium-dairy (APMD) group consumed 3—4 servings of dairy products per day in addition to vegetable protein sources to increase their total protein intake to 15%. Participants in the high-protein/high-dairy (HPHD) group consumed 6—7 servings of dairy products per day resulting in a daily protein intake of 15%. These women derived an additional 15% from vegetable sources, bringing their total protein intake to 30% of total energy intake. In the randomization procedure the groups were stratified by BMI (27—29, 30—34 and 35—40 kg/m2) such that all three groups comprised equal numbers of women from all three BMI categories. At the onset of the study as well as after 8 and 16 weeks body fat and fat-free mass of the participants were measured by DEXA (dual-energy X-ray absorptiometry). In a subset of 39 participants the quantity of visceral adipose tissue was determined through MRI scans at baseline and after 16 weeks.
Most fat mass lost in the HPHD group During the study the participants' body weight dropped in the three groups at a similar pace (—4.3±0.7 kg (P<0.05) on average in 16 weeks' time). The decline in BMI was also similar for the three groups (—1.8±0.3 kg/m2 (P<0.05) on average). Likewise, waist circumference decreased in all three groups (—4.9±0.9 cm (P<0.05) on average). Loss of body fat was highly significant (P<0.01) in all three groups. Figure 1 shows that the loss of body fat was significantly greater in the HPHD group than in both other groups. The graph also shows that fat-free body mass increased in the HPHD group by an average of 0.7±0.3 kg in 16 weeks' time (P<0.05). Fat-free body mass did not change in the APMD group and declined in the APLD by an average of —0.7±0.3 kg in 16 weeks; P<0.05). Figure 2 shows that truncal fat mass and fat volume decreased in all three groups, declines being greatest in the HPHD group; these variables differed significantly between the HPHD and the APLD group. An analysis of the whole study sample revealed that both calcium intake and protein intake correlated in the 16th week of the study with changes in body fat, truncal fat mass and truncal fat volume.
Improved cardiovascular fitness Cardiovascular fitness improved in all three groups. The average reduction in pulse between the start and the conclusion of the study was ca. 15 beats per minute (P<0.05). In all three groups muscular strength improved. For some (but not all) exercises the increase in muscle in the HPHD group was significantly stronger than in the APLD group. The researchers hold it possible that this effect is associated with the increase in muscular mass in the group with the highest protein intake from dairy products (the HPHD group). This assumption corresponds with the outcomes of a study by the same research group published in 2010 (3). That study showed that milk consumption as compared to consumption of an isoenergetic carbohydrate drink improves muscular strength in women engaged in resistance training. In the discussion in their 2011 paper, Josse et al. underline that a higher consumption of dairy products and a higher protein intake are associated with more body fat loss and even an increase in fat-free mass for overweight and obese women after a hypoenergetic period. These effects are seen as early as after 16 weeks. Their findings are in keeping with the results of a meta-analysis of studies of the association between calcium intake and body weight in postmenopausal women (4). They conclude that a high protein intake, , notably protein from dairy products, combined with energy restriction and anaerobic and resistance training can contribute appreciably to improved body composition during a period of weight loss.
A.R. Josse, S.A. Atkinson, M.A. Tarnopolski, S.M. Philips (2011) Increased consumption of dairy foods and protein during diet- and exercise-induced weight loss promotes fat mass loss and lean mass gain in overweight and obese premenopausal women. J. Nutr. 141:1626—1634.
A.R. Josse, J.E. Tang, M.A. Tarnapolski, S.M. Phillips (2010) Body composition and strength changes in women with milk and resistance exercise. Med. Sci. Sports Exerc. 42: 1122—1130.
I.J. Onakpaya, R. Perry, J. Zhang, E. Ernst (2011) Efficacy of calcium supplementation for management of overweight and obesity: systematic review of randomized clinical trials. Nutr. Rev. 69: 335—343.