The investigators' hypothesis is that a plant-based diet may be beneficial if nutritional deficiencies will be corrected. The aims of the present proposal are to 1) study endothelial functions of subjects on well-defined vegetarian/vegan diets compared to age and sex matched omnivores (controls), and 2) study the differences in energy expenditure, body composition, overnight substrate utilization, blood work results, and levels of intracellular reactive oxygen species (ROS) and of adhesion molecules on the different diets.

The serious doubts about the nutritional adequacy of vegetarian diets in the past were essentially put to rest by recent studies that suggested that plant-based diets are healthy and associated with lower risk of several chronic diseases. Nevertheless, various nutritional deficiencies have been identified, and it has been shown that individuals who follow different types of vegetarian/vegan diets may not experience the same effects on their health.

Working Hypothesis

1. Vegetarian/vegan diets will promote protection against cardiovascular risk factors if supplemented with possibly deficient nutrients.
2. There will a further protective effect and a greater number of differences between subjects following a vegetarian diet compared to those following a vegan diet.
3. Higher energy expenditure and lower and different caloric intake will promote a favorable difference in body composition (lower body fat) via a different substrate utilization expressed in the measured respiratory quotient (RQ).
4. Extra- and intracellular free radicals will be higher in subjects who adhere to vegetarian/vegan diets compared to omnivores.

Aims of the study

1. To study the effect of vegetarian/vegan diets on endothelial functions after correcting for modifying factors.
2. To study the effect of the above-mentioned plant-based diets on carotid intima-media thickness.
3. To study the differences in body composition, resting energy expenditure and over-night substrate utilization between the different diets.
4. To study the intracellular ROS of subjects following different diets.

Inclusion Criteria:

• over 5 years' adherence to any type of diet
• age range 35-50 years
• BMI ≤32

Exclusion Criteria:

• smoking
• type I and II diabetes
• liver and kidney impairments
• cardiovascular diseases
• patients with tumors
• patients on medications which may affect cardiovascular parameters (including 5 phosphodiesterase inhibitors, beta blockers, ACE inhibitors and others)
• BMI >32 kg/m2.