Diet-induced Arrangement of the Gut Microbiome for Improvement of Cardiometabolic Health
Condition: Overweight; Obesity
MeSH terms: Overweight
Study type: Interventional

Summary: 
      Mediterranean diet (Med-D) has been recognized as an intangible cultural heritage by UNESCO
      and was shown to be beneficial for the treatment of obesity, type-2 diabetes and
      cardiovascular diseases. Individuals with the highest adherence to Med-D (classified
      according to Sofi et al., 2010) were characterized by increased levels of specific
      fibre-degrading bacteria, increased faecal levels of short chain fatty acids, and lower
      urinary concentrations of the atherogenic compound TMAO. However, the interplays between
      Med-D and microbial populations in the intestine remain unclear. Moreover, a number of
      clinical conditions like obesity, T2D, and atherosclerosis are associated with dysbiotic
      microbial ecosystems in the gut, i.e., shifts in the structure and function of the
      microbiota, but the characteristic features of dysbiotic gut communities and the impact of
      diet are not very well defined. The present study will evaluate the impact of Med-D on
      cardiometabolic health in human subjects via modification of intestinal microbial communities
      and its impact on health outcomes, mainly related to inflammatory, oxidative and hormonal
      status, in overweight subjects.
    

Detailed description: 
      It is estimated that in 2050 approximately 40-50% of the adult population worldwide will be
      overweight/obese (BMI > 25/30 kg/m2), with 10-20% of them developing insulin resistance
      resulting in metabolic syndrome and type-2 diabetes (T2D). T2D is forecast to become the 7th
      leading cause of death worldwide by 2030. Obesity and T2D are major risk factors for the
      development of cardiovascular diseases CVD. Despite currently available therapeutic
      strategies to reduce cardiovascular risk, less than one third of all cardiovascular events
      can be prevented. Hence, cardiovascular complications associated with obesity and metabolic
      syndrome/T2D are major health issues in Western societies, representing a substantial
      societal and economic burden (40 % of all deaths in Europe and EUR 196bn/y) that cannot be
      solved by the currently available treatment paradigms. Based on the close relation between
      CVD and diabetes mellitus, these two diseases together are referred to as cardiometabolic
      diseases (CMD). With respect to prevention strategies, it is crucial to understand molecular
      mechanisms that regulate transition phases from obesity and T2D to CVD. In particular,
      environmental factors (primarily diet and gut microorganisms) that promote or retard the
      development of cardiovascular complications must be identified in order to propose novel
      preventive strategies for maintaining cardiovascular health. Recent data showed that the
      communities of microorganisms in the intestine (gut microbiota) have a substantial impact on
      systemic cardiometabolic regulation, inflammatory activation and eventually CVD. Defining
      diet-microbiome profiles that contribute to resistance towards CMD development would be a
      major step forward in the field of nutritional disease prevention. Western dietary patterns,
      characterized by high consumption of red and processed meat, refined cereals and sugars, and
      high-fat dairy products, have been associated with a high incidence of CMD in Western
      countries. In contrast, the Mediterranean diet (Med-D) is a nutritionally recommended dietary
      pattern characterized by high-level intake of fruit, vegetables, legumes, nuts, minimally
      processed cereals, moderately high consumption of fish, low intake of saturated fat, meat and
      dairy products, regular but moderate consumption of alcohol and extra virgin olive oil as the
      main fat. Med-D has been recognized as an intangible cultural heritage by UNESCO
      (www.unesco.org/culture/ich/RL/00884) and was shown to be beneficial for the treatment of
      obesity, T2D, and CVD. Moreover, data from an Italian observational study including 153
      subjects with different dietary regimens (omnivores, vegetarians, vegans) showed that
      individuals with the highest adherence to Med-D (classified according to Sofi et al., 2010)
      were characterized by increased levels of specific fibre-degrading bacteria, increased faecal
      levels of short chain fatty acids, and lower urinary concentrations of the atherogenic
      compound TMAO. However, the interplays between Med-D and microbial populations in the
      intestine remain unclear.

      In this framework, the present project will focuses on the impact of diet on maintaining
      cardiometabolic health in human subjects via modification of intestinal microbial
      communities. Specific aims of the study are to establish new targeted intervention for
      maintenance of cardiometabolic health and thereby test the causal relationship between diet
      and the gut microbiome; to study the functionality of the intestinal milieu via meta-omics
      approaches, aiming at harmonization via standardization effort. The study will includes the
      establishment of a 2-months dietary intervention with an isocaloric Mediterranean diet
      (Med-D). Coupled with detailed host phenotyping and gut microbiota profiling during and after
      intervention, this will allow assessment of the causal effects of diet and the gut microbiome
      in populations at high risk for CVD.

      Subjects in the Med-D group will be assigned a personalized diet prepared on the basis of own
      eating habits as established by 7-d food diary recalls. Energy values and whole macronutrient
      composition of habitual diets will be kept unchanged during Med-D intervention. However,
      changes in carbohydrate (dietary fibre vs. starch), dietary fat (saturated vs.
      mono/polyunsaturated fatty acids), and protein (vegetable vs. animal) composition will be
      applied. Briefly, Med-D will be prepared so as to achieve: 1) 2 % increase in energy from
      dietary fibre, mainly by replacing refined wheat products with wholegrain wheat products
      and/or with fruit/vegetables; 2) a repartition of energy from fat 1:3:1 (saturated :
      monounsaturated : polyunsaturated), replacing animal by vegetable fat and
      introducing/increasing virgin olive oil consumption; 3) a repartition of energy from proteins
      1:4 (animal : vegetable proteins), replacing meat and/or dairy products by legumes. Control
      subjects will not change their habitual diet during intervention. All subjects will be
      requested not to change physical activity levels during the 8 week intervention period.
      Compliance will be assessed every 2 weeks by self-recorded 4-d (3 working and 1 weekend days)
      food diaries and by International Physical Activity Questionnaire (IPAQ). At baseline, after
      1 month and after 2 months from starting the protocol, blood drawings will be performed and
      urine and feces will be collected from fasting subjects.

      In a subgroup of participants the postprandial blood glucose and lipid response will be
      evaluated after a test meal resembling the lunch of the Mediterranean or the Control diet
      according to the assigned diet. Test meals will be performed at baseline and at the end of
      the intervention with samples taken at fasting and for 4 hours after the meal for
      determination of glucose, insulin, lipids, and SCFA.

      Further analysis of compliance will be conducted based on metabolomics, allowing
      discrimination of animal/vegetable protein, olive oil intake and increased intake of foods
      with phenolics. Metabolomes (well known to reflect both diet and microbial metabolism) will
      also be compared between categories in order to identify protective or risk profiles using
      both bioinformatics and chemometrics approaches. Metagenomes will be analysed following SOPs
      utilized in landmark studies already published. Comparison of pre-defined groups of
      individuals will allow identification of microbial genes that have different abundances in
      the groups (e.g. twins discordant for CMD). Further, genes will be associated to continuous
      variables of clinical and nutritional interest (e.g. insulin sensitivity, intake of specific
      dietary components) by covariance analysis. Concatenated datasets of physiological output
      data, metagenomic and metabolome profiles from the intervention studies to predict subsets of
      features by multivariate analysis (PLS-DA) that can classify subjects according to their
      relative adherence to a Med-D. The profile will be used to probe the microbiome for specific
      alterations as a function of the interventions.

      The sample size needed to detect an effect of Med-D on individual antioxidant and
      inflammatory markers is defined on the basis of a previous study conducted by UNINA showing
      that 30 participants in each treatment group would give sufficient power (a-error 0.05, 80%
      power, 2-sided testing) to detect a 50% change in urinary and fecal ferulic acid and a 30%
      change of fasting TNF. In addition, it is estimated that a sample size of 28 participants
      would be adequate to detect a 10% change in fasting total cholesterol by using variation in
      accordance with other studies. The number of participants will be increased to 40 per group
      to compensate for dropouts. Samples (faeces, venous blood, and non-acidified 24h urine) will
      be collected at baseline, 4 and 8 weeks after starting dietary intervention.
    

Intervention name(s): Mediterranean diet; Control Diet
Intervention type(s): Other; Other
Intervention description(s): Subjects in the Med-D group will be assigned a personalized diet prepared on the basis of own eating habits as established by 7-d food diary recalls. Energy values of habitual diets will be kept unchanged during Med-D intervention. Briefly, Med-D will be prepared so as to achieve a weekly consumption of:
7 portions of milk or yogurt plus whole grain cereals,
7 portions of nuts (30g)
At least 3 portion of absolute legumes
14 portions of vegetables
21 portions of fruit
4 portions of whole grain pasta
3 portions of whole grain pasta with vegetables or legumes
7 portions of whole grain bread
3 portions of fish
Extravirgin olive oil as unique source of discretional fats All subjects will be requested not to change physical activity levels during the 8 week intervention period.; Control subjects will not change their habitual diet during intervention. All subjects will be requested not to change physical activity levels during the 8 week intervention period.
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Single (Participant)
Primary purpose: Treatment
Keywords: cardiovascular diseases; gut microbiota; Mediterranean diet