The Influence of Animal- or Plant-Based Diets on Blood and Urine Trimethylamine-N-Oxide (TMAO) Levels in Humans.

PURPOSE OF REVIEW: The aim of the review was to evaluate which diets are associated with higher TMAO levels. RECENT FINDINGS: Several studies have shown that plasma and urinary levels of trimethylamine N-oxide (TMAO) are a reliable indicator of cardiovascular disease risk. Diet certainly has a strong influence on TMAO levels, but there is still uncertainty about which diet is the most effective in reducing this risk factor. PubMed, Web of Science and Scopus were searched for studies that were published up until July 1, 2021 using specific keywords. In total, 447 studies were evaluated, of which papers on individual foods or supplements, or conducted in children, in vitro or in animal model studies were excluded. Twenty-five studies were included in this review. Three studies showed that caloric restriction and (visceral) weight loss improve TMAO levels. Six out of eight studies revealed beneficial effects of plant-based diets on plasma or urinary TMAO concentrations. Most of the studies demonstrated that a diet high in protein, particularly of animal origin, such as diets rich in fish or red meat, have negative effects on TMAO levels. Most studies that have evaluated the relationship between diet and plasma or urinary concentrations of TMAO seem to indicate that plant-based diets (Mediterranean, vegetarian and vegan) are effective in improving TMAO levels, while animal-based diets appear to have the opposite effect. Further long-term studies are needed to assess whether vegetarian or vegan diets are more effective than the Mediterranean diet in reducing TMAO levels.

Association of Urinary and Plasma Levels of Trimethylamine N-Oxide (TMAO) with Foods.

INTRODUCTION: Trimethylamine N-oxide (TMAO) may play a key mediator role in the relationship between the diet, gut microbiota and cardiovascular diseases, particularly in people with kidney failure. The aim of this review is to evaluate which foods have a greater influence on blood or urinary trimethylamine N-oxide (TMAO) levels. METHODS: 391 language articles were screened, and 27 were analysed and summarized for this review, using the keywords "TMAO" AND "egg" OR "meat" OR "fish" OR "dairy" OR "vegetables" OR "fruit" OR "food" in December 2020. RESULTS: A strong correlation between TMAO and fish consumption, mainly saltwater fish and shellfish, but not freshwater fish, has been demonstrated. Associations of the consumption of eggs, dairy and meat with TMAO are less clear and may depend on other factors such as microbiota or cooking methods. Plant-based foods do not seem to influence TMAO but have been less investigated. DISCUSSION: Consumption of saltwater fish, dark meat fish and shellfish seems to be associated with an increase in urine or plasma TMAO values. Further studies are needed to understand the relationship between increased risk of cardiovascular disease and plasma levels of TMAO due to fish consumption. Interventions coupled with long-term dietary patterns targeting the gut microbiota seem promising.

The different daily distribution of proteins does not influence the variations in body composition in a sample of subjects undergoing a low-calorie Mediterranean-type diet.

BACKGROUND: Controversy exists regarding whether the different daily balances of proteins between meals and snacks in a low-calorie diet may influence the effects on body composition (BC) results. Aim of this study is to evaluate BC changes made by a lifestyle intervention in a randomized homogeneous sample of two groups with equal daily caloric reduction but different protein distributions between meals. METHODS: Forty-seven men and women (mean age: 32±10 years; Body Mass Index: 28.4±2.4 kg/m2) consumed an energy-restricted diet (788 kcal/d below the requirement) for eight weeks in a free-living contest. Subjects consumed 90.1 g protein/d (1.10±0.16 g/kg/day) and were randomized in an EVEN (16.7% at breakfast, 32.8% at lunch, 31.3% at dinner, 19.2% at snacks; N.=23) or UNEVEN (15.4% at breakfast, 36.6% at lunch, 34.9% at dinner, 12.4% at snacks; N.=24) distribution pattern. The nutritional characteristics and caloric deficit of the two diets were similar. RESULTS: The total sample had an overall improvement in both BMI (-0.9±0.6) and fat mass (FM: -2.3±1.5), while lean body mass was preserved (LBM: 0.0±0.7). There were no significant differences between the two groups in variations in BC. CONCLUSIONS: In overweight and obese subjects undergoing a Mediterranean-type low-calorie diet, a different distribution of daily protein intake between meals and snacks does not result in significant differences in terms of FM loss and LBM maintenance. This is one of the first studies showing that nutritional dietary plans with different daily protein distribution show no particular differences in fat loss and lean mass maintenance.

Effects of Quality and Quantity of Protein Intake for Type 2 Diabetes Mellitus Prevention and Metabolic Control.

PURPOSE OF REVIEW: The aim of this review is to evaluate the ideal protein quality and quantity and the dietary composition for the prevention and metabolic control of type 2 diabetes mellitus (T2DM). INTRODUCTION: Although some reviews demonstrate the advantages of a diet with a higher protein intake, other reviews have observed that a diet high in carbohydrates, with low-glycaemic index carbohydrates and good fibre intake, is equally effective in improving insulin sensitivity. METHODS: Over 2831 articles were screened, and 24 from the last 5 years were analysed and summarised for this review, using the protein, diabetes and insulin glucose metabolic keywords in Pubmed in June 2019. RESULTS: Eleven studies demonstrate that a higher consumption of proteins has a positive effect on insulin sensitivity. A higher intake of animal protein seems to be related to an increased risk of T2DM. Four studies show that consumption of meat has a deleterious effect. Higher intake of plant protein and dairy products is associated with a modestly reduced risk. DISCUSSION: Based on the results obtained, for the prevention of T2DM and all disorders related to metabolic syndrome, no ideal dietary composition has yet been found. The advantage of plant protein sources may be related to the foods' low-glycaemic index due to the high fibre content. However, the right protein quality (animal and plant) and the quantity for T2DM prevention and metabolic control are unclear and need to be investigated with further long-term studies.

Diet high in protein-rich foods with structured sport activity may be useless to lose fat mass and maintain fat-free mass.

BACKGROUND: The aim of this study was to demonstrate that a normal protein diet along with minimal sports activity can be enough to lose fat mass and maintain muscle mass. METHODS: All participants were prescribed a hypocaloric nutritionally balanced Mediterranean-style diet tailored to the individual for 8 weeks. Body composition and energy expenditure were measured. Sedentary patients (G1) were only recommended to perform minimal aerobic training, while sport subjects (G2) were prescribed structured physical activity and higher calorie and protein contents in the diet. RESULTS: There were no significant differences between the two groups for any of the measured parameters. CONCLUSIONS: The models of lifestyle changes that are currently circulating were for the most part ineffective. It does not appear to be necessary to increase the protein content of the diet above that recommended by guidelines in order to lose weight. Even prescribing specific physical activity is not necessary to maintain muscle mass.

Losing Weight after Menopause with Minimal Aerobic Training and Mediterranean Diet.

OBJECTIVE: It is a common belief that menopausal women have greater difficulty losing weight. The aim of this study was to assess the efficacy of a Mediterranean diet (MD) to promote weight loss in postmenopausal women. All participants were prescribed a hypocaloric traditional MD, tailored to the individual. Subjects were asked not to begin any kind of physical activity. Body composition was measured at the beginning and after 8 weeks of treatment. In total, 89 women (age 52.8 ± 4.5 years, BMI 30.0 ± 5.2 kg/m2, fat mass 31.6 ± 10.5 kg) were divided into two groups: the first group consisted of fertile women over 45 years of age, the second group consisted of those diagnosed as menopausal. All women had an improvement in body composition (fat mass -2.3 ± 2.1 kg, p < 0.001; protein -0.1 ± 0.7 kg, p = 0.190) and blood pressure values. No differences were found between the two groups except for a higher reduction of low-density lipoprotein in the menopausal group (p = 0.035). A positive significant correlation between plant to animal protein ratio and fat-free mass variation was found in the menopausal group. These data suggest that a high adherence to a traditional MD would enable menopausal women to lose fat mass and maintain muscle mass with no significant difference to younger women. Fat mass reduction provides menopausal women with improved cardiovascular and metabolic risk factors.