Back in the '80s, I remember that at the races of "dilettanti" (now under-23) I could see a lot of riders from the East, especially Russians, eat bread and salami with gusto, under the astonished and critical gaze of our technical experts and riders. 
Needless to say that back then, russian cyclists coming over were dominating the racing scene, but the credit was attributed to some kind of "practice". 

For a couple of years now the role of nitrates in sports performance has become becoming increasingly topical. 
Nitrates are found in nature, especially in green leafy vegetables (spinach, chard, arugula, lettuce, celery) and beetroot. 
They have been used for centuries as a preservative in meat sausages (hence the connection with the eating habits of russian riders), in the form of nitrate and sodium nitrite. 

The ingested nitrates are absorbed in the intestines, are then concentrated at least tenfold in the saliva (thus explaining the practice of a particular ProTour team of holding some beans in the mouth for 40mins) and in the mouth are transformed into nitrites by bacteria that are located on the tongue. 
Nitrites are then partially converted to Nitric Oxide (NO) which is the main responsible for the effects of nitrate on metabolic functions. 

There is also an endogenous production of NO, at endothelial level, starting from the amino acid L-arginine. The magnitude of this production is genetically determined and decreases with age. 

Since 2007, Scandinavian (Acta Physiol 2007; 191:59-66) and English (J Appl Physiol 2009; 107:1144-1155) studies demonstrated a reduction of about 10% in oxygen consumption for workloads of medium intensity after an intake of 600mg (in three separate doses) of sodium nitrate per day, for three days. 
The same result was confirmed after a single intake of 0.5 liters of beetroot juice, with a reduction in the cost of oxygen from 10 to 9 ml/min/watt (Am J Physiol 2010; 299: R1121-1131). The effect was maintained for 15 days if the assumption was repeated daily. 

It seems that nitric oxide enhances the efficiency of muscle contraction through a reduction in the cost of the actin-myosin interaction (J Appl Physiol 2010; 109:135-148) and an improvement in the efficiency of mitochondrial respiration (Cell Metabolism 2011; 13 :149-159). 

The single intake of 0.5 liters of beetroot juice led to an improvement of 6% in the power generated in a trainer-simulated 16km time trial in a group of mid-level cyclists (VO2max = 56 ml/kg/min), as shown in a English double-blind study (Med Sci Sports Exerc 2011; 43:1125-1131). 
This improvement, more than negligible, corresponds to 48 seconds (3"/km) and is comparable with the result of a transfusion of a pint of blood. 

Another British study (J Physiol 2011; 589:5517-5528) showed a further performance enhancement at ALTITUDE after an intake of 0.75 liters of beetroot juice in the 24 hours preceding the test, demonstrating a greater conversion of nitrite to nitric oxide in hypoxic conditions. 
Tibetan people living above 4000m of altitude showed endothelial production of endogenous NO ten times higher than normal, allowing them to compensate hypoxia with a concentration of Hb = 16.5g; compared to the inhabitants of the Andes at similar elevations, who are forced to compensate with much higher Hb concentrations (18-19g), this shows a greater efficiency in the use of O2 allowed by nitric oxide (Proc Natl Acad Sci USA 2007, 104:17593-17598). 

The protocols for supplementation with nitrates have not yet been clearly defined, but they certainly should be personalized, and those who have already developed them surely prefer to keep them close to the chest. 

However, some of the information may already be disclosed: 

- 0.5 liters of beetroot juice or 600mg of sodium nitrate are sufficient to approximately double the circulating nitrite and show the effects on performance 1.5-3h after the single dose 

- this effect persists for 6-8 hours and can be replicated for at least 15 days 

- nitrates naturally contained in plants are preferred to synthetic products (sodium nitrate) as in vegetables there are antioxidants (vit C in particular) that are able to counteract the negative effects of nitrite in the stomach 

- before and after the intake of nitrates avoid the rinse of the oral cavity with antibacterial solutions, as well as the use of toothpaste and medicated chewing gum in order to preserve the bacterial flora which transforms nitrates into nitrites. After the intake it is useful to stimulate saliva for 40-60 min (like holding the famous dried beans in the mouth...) 

- the use of nitrite, intentionally or accidentally, is dangerous: the lethal dose LD50 is a little more than 100mg/kg (7g can kill a man ...).