The Principles of Ayurveda are based on universal laws. One of them is similarity in governing of universe and body of all living beings. The universe is governed by properties of- Solar, Lunar and Air through Sun, Moon and Air, which is represented as Pitta, Kapha and Vata In all living being. Thus it is obvious that any change in the environment has its effect on all living beings.
This relation of governing principles of universe and living body can be understood through the concept of Ritucharya (the specific period of time to be followed), which has close relation for healthy life. For the convenience of human, a one year period of time is called Samvatsar. This one year period of time is divided in Uttarayana (movement of Sun towards northern region) and Dakshinayana (movement of Sun towards Southern region). Each of them are having three Ritus (seasons)- Sisira, Vasant and Grisma (Uttarayan) and Varsha, Sarad, Hemant (Dakshinayan). Each Ritu is having two months consisting of total sixty days, which are equally divided into thirty days for each month. While moving towards northern region the intensity of heat enhances in that region with the result of the strength of living being (plant and animal kingdom) is reduced due to absorption of nutritional substances which has been said as Snigdha.
On the contrary of that in Varsha, Sarad and Hemant due to gradual reduce in intensity of heat and improve in properties of Moon, thereby strength of all living being enhances successively and it is maximum during Hemant Ritu. The properties of Air act as catalyzer and vitiate heat and cold in association with Sun and Moon respectively. Those thirty days have two half of fifteen days each based on visibility and non visibility of Moon i.e., Sukla paksha and Krishna paksha respectively.
Every living being requires two things for long lasting survival with healthy life. The first and foremost is wholesome food and a congenial surrounding atmosphere. In fact ritucharya gives guidelines to live in a particular season with favourable dietary regimen which protects health in different seasons. The ancient concept of diet has been scientifically provedby the western scientist.

According to Glenn R Gibson of United Kingdom that the main role of diet is to provide nutrients to meet host physiological requirements. As research behind diet and health has evolved, so has the concept of 'functional foods' become popular. Foods which are touted as being 'functional' are thought to exert certain positive properties over and above their normal nutritional value. While not universally popular and sometimes plagued by inadequate research/claims, the concept is certainly commercially successful, e.g. The Institute of Grocery Distributors ( estimates that the functional food market in the UK in 2007 will have annual sales worth around £1800m.
This shows an exponential rise from the 1996 figure of £134m. Examples of functional foods include organic and inorganic micronutrients, vitamins, anti-oxidants, dietary fibre, some proteins (e.g. lactoferrin), certain bioactive peptides and polyunsaturated fatty acids.

Recent years have seen a major change in how activities of the human gastrointestinal tract are perceived. This has been driven by increased knowledge of the gut microflora composition and activities. This has been helped by a shift away from traditional microbiological culture methods to the use of molecular markers of culture identity. The colon is the most heavily populated region of the gastrointestinal tract and, because of this resident microbiota, is one of the most metabolically active organs in the body. The concept of modulating activities directed towards improving gut microbial function has a long history, as diet can have a major effect on the gut microflora activities. Whilst some indigenous bacteria can be pathogenic (e.g. proteolytic clostridia and bacteroides), it is also the case that some genera / species may offer health promoting attributes. For example, bifidobacteria and lactobacilli are thought to exert powerful antipathogenic effects and are mainly responsible for 'colonisation resistance' in the gut. Moreover, the same genera have been attributed with other beneficial aspects: such as protection from bowel tumours and metabolism of cholesterol and other lipids in the gut. Whilst many of the health promoting aspects have yet to be definitively proven in humans, it would appear that there is value in eliciting a change away from a gut flora dominated by potentially harmful bacteria towards a more benign, or beneficial, composition.

In fact, the seasonal regimen has close relation with the concept of Agni (digestive fire), which not only transform the food substances into nutrition but also gives strength to the living body. Apart from that it also helps in multiplication of beneficial bacterial growth in the body.