Dietary Modification Clinical Trial
Official title:
Effect of a 6-month Vegetarian Diet in Omnivorous Women on Body Creatine, Carnitine and Carnosine Stores
Balanced vegetarian diets are popular and contain health-promoting characteristics. A
balanced lacto-ovo-vegetarian diet differs in nutrient intake from an omnivorous diet, e.g.
by increased intake of fibre, magnesium and antioxidants, but lower intake of omega-3 fatty
acids and vitamin B12. However, the impact of reduced to near absent intake of carnitine,
carnosine and creatine in a vegetarian diet is less well established and could be relevant in
relation to muscle function, exercise capacity and sports performance. Few longitudinal
intervention studies investigating the effect of a vegetarian diet on the availability of
these compounds currently exist.
This study aimed therefore to investigate the effect of of transiently switching omnivores
onto a vegetarian diet for 6 months on muscle and plasma creatine, carnitine and carnosine
homeostasis.
We hypothesized that homeostasis of creatine and carnosine would be disrupted when their
dietary intake was missing. For carnitine, however, we hypothesized that homeostasis can be
maintained given its slow turnover rate and its presence in some non-meat nutrients. A second
aim was to investigate whether supplementation of creatine and beta-alanine (the
rate-limiting precursor of carnosine synthesis), concurrently with a lacto-ovo-vegetarian
diet, was able to correct for potentially emerging deficiencies.
Forty healthy female omnivores will be included in this 6-month intervention study. Exclusion
criteria are smoking, chronic use of medication, athletes participating in competitions,
vegetarianism or eating meat or fish less than 5 times a week. The study is scheduled over a
period of 6 months and measurements will be performed 1 week prior to the intervention (0M),
after 3 months (3M) and within the last week (6M). Ten women will continue their omnivorous
diet throughout the entire study (controls) and the other 30 subjects will switch to a
lacto-ovo-vegetarian diet for 6 months. The vegetarian group will be split in 2 groups,
matched for age, weight, height and baseline carnosine concentrations in soleus and
gastrocnemius medialis muscles. Fifteen of them will be supplemented with beta-alanine and
creatine (Veg+Suppl) and the other 15 women will receive a placebo (Veg+Pla). A co-worker,
not involved in the study design and analysis, will perform the randomisation and will
prepare the containers with supplements. With regard to supplementation, the study is
double-blind placebo-controlled. The lacto-ovo-vegetarian diet consists of vegetables,
fruits, seeds, grains, meat substitutes, eggs and dairy products and the exclusion of meat,
poultry and fish. Subjects will complete a 3 day food diary at the start and after 3 months
and will receive nutritional advice by a dietician during the study to prevent deficiencies
in macronutrients and micronutrients. Furthermore, vegetarian recipes will be provided by
email to support the subjects in their vegetarian diet.
The supplementation protocol includes simultaneously daily oral administration of creatine
monohydrate (Creapure®, AlzChem AG, Germany) and slow-release beta-alanine (Carnosyn®,
Natural Alternatives International, San Marcos, USA) or a placebo (maltodextrin, Natural
spices, France). The supplements are considered as safe and efficacious. The Veg+Suppl group
ingests 1 g of creatine monohydrate (2 capsules of 500 mg) and 0.8 g of beta-alanine (1
Carnosyn® tablet) each day during the intervention period. The Veg+Pla group will be
supplemented with an identical number of capsules and tablets of maltodextrin. All subjects
are asked not to take any other supplements than those provided by the current study.
Compliance will be checked by asking the subjects to return the containers and counting the
pills that are left. The control group, who will remain on an omnivorous diet, will not
receive any supplements.
Before (0M), after 3 (3M) and 6 months (6M), subjects will perform an incremental cycling
test, a fasted venous blood sample and 24hr urine will be collected, a muscle biopsy of the
vastus lateralis muscle will be taken and muscle carnosine content will be determined by
1H-MRS.
A two-way analysis of variance (ANOVA) will be used to evaluate plasma and urinary metabolite
concentrations, muscle carnosine, muscle biopsy metabolite concentrations, time to exhaustion
(TTE) and VO2max with 'group' (Veg+Suppl; Veg+Pla; control) as between-subject factor and
'time' (0M; 3M; 6M) as within-subject factor (SPSS statistical software, SPSS Inc, Chicago,
USA). For the analysis of capillary lactate and pH, measurements before and after the
incremental cycling test were included as another within factor (start; end). In case of
significance, analyses were repeated for each group separately and pairwise comparisons were
used to compare the different time points. Values will be presented as mean ± SD and
statistical significance threshold will be set at p ≤0.05.
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