Background: A well balanced diet is important for normal function of endothelial cells. Diets high in fat and/or calories can lead to hypertriglyceridemia and postprandial lipidemia and thus are considered a risk factor for the development of atherosclerosis. Big meals may result in chronic elevations in the level of atherogenic lipoproteins as well as evoking chronic inflammatory response. Both may lead to pathological changes on the arterial vessel wall and myocardium. Objective(s): To study the effect of the size of a well-balanced meal on the lipid profile in the post prandial state and its effect on the endothelial function, ventricular filling and diastolic function. Methods: one group pretest-posttest study was carried out on 40 young healthy lean volunteers aged 30 to 39 years who after overnight fast were invited to eat a big breakfast meal. Postprandial blood samples were then drawn after 3-4 hours to determine changes induced by the big meal in the blood.  On the following day, the same procedure was adopted but with a breakfast meal which contains only one third of the size of the big meal (small meal). The items of comparison between the two meals included: The changes induced by both types of meals on the lipid profile of the blood by assessing the postprandial levels of TG, TC, LDL-C, HDL-C and FFAs; assessment of the inflammatory response by assessing postprandial levels of CRP; The changes induced on endothelial cell functions by assessing the postprandial levels of ET1 and NO; and the changes induced by the two types of meals on the left ventricular function as determined by echo Doppler as well as tissue Doppler imaging (TDI). Results: The big meal was associated with elevations in TG, TC, LDL-C, CRP, ET1 and NO (P=0.001, 0.021, 0.057, 0.110, 0.002, 0.001respectively). The small meal showed significant increase in levels of HDL-C (P=0.001) and FFAs (P=0.048). The diastolic function of the left ventricle showed significant reduction after the ingestion of the big meal versus the small meal. Conclusions: The study concluded that big meal size negatively impact lipid homeostasis and endothelial function and the recognition of this possible danger of big meals can lead to the possibility of prevention of atherosclerosis through controlling of the meal size.