We are all supposed to include three cups - or six servings - of vegetables in our daily diet. Unfortunately, most of us fail to do so. And that is why some of us take the quick and easy way out by drinking vegetable juice instead.

According to research by the Stanford Cancer Institute in California, the US, a cup of carrot juice is equivalent to five cups of minced carrot. Carrot juice is loaded with potassium, folate, vitamins A and C, and beneficial phytochemicals. It has minimal calories, almost no fat and is a source of plentiful energy. If you are too busy for breakfast, a glass of juice can recharge you, while keeping your weight and blood pressure under control.

This, however, does not mean you can give up cooking altogether and replace your meals with glasses of fresh vegetable juice. While veggie juice - also called green juice - has its benefits, there's a long list of harmful effects too.

Problem pack

The benefits discussed above are true only of fresh juice from chemical-free veggies. As soon as you opt for packed juice - which is always pasteurised - you lose most nutritional benefits. Besides, even if "no added sugar" is written on the pack, fructose - a sugar found in fruits - is added to enhance taste, which is harmful for diabetics.

Also, preservatives are added to packed juice to prolong shelf life. There is no harm done if these are in the right proportion, but in India preservatives are not added following the rule book, says dermatologist Dr Sanjay Ghosh. "Many juices are found loaded with artificial colour and flavour that cause allergy and skin rash," he adds.

Worm factor

Fresh juice extracted at home should be safe, right? Wrong, because those lush vegetables you just bought at the market may have been grown in contaminated soil, or they could be carrying contagions, worms (tape or hook) and pesticide residues. In fact, its "freshness" itself may be the handiwork of an adulterant or harmful colours. The shiny tomatoes, bright green peas and lush leafy vegetables might look tempting, but underneath lie something sinister - a toxic cocktail of hazardous chemicals - which contravenes their nutritional benefits.

Chemicals such as copper sulphate, rhodamine oxide, malachite green and carbide are most commonly used for colour and freshness. These are neurotoxic and carcinogenic. Some are toxic to the liver and kidney. They may cause moderate to severe allergic reactions as well as hasten ageing.

Sometimes hormone injections, mainly oxytocin, are used to speed up the growth of certain vegetables. These may cause hormonal imbalance as well as harm the reproductive system in humans. Some vegetable vendors rub petroleum oil on vegetables such as brinjal and tomatoes to give them a shiny look. Ingesting them has a toxic effect on the respiratory and gastrointestinal systems. Therefore, the question of consuming these shiny vegetables as juice does not arise.

If you have been prescribed a low-potassium diet to protect yourself from heart and kidney ailments, green juice will be harmful for you, too. If you have hypothyroidism, avoid green juice after a dose of thyroxin; otherwise the medicine loses its efficacy.

"The most common problem we encounter in those who have green vegetable juice is worms in the intestine and even brain. Even if you wash the veggies in warm water, the worms may persist," says Dr Indranil Saha, a consultant gastroenterologist in Calcutta. "Besides - since juice is devoid of fibre - if you consume it on a regular basis you may have constipation, bloating, flatulence and indigestion. You can have a glass or two of fresh juice in a week. And make sure you extract the juice at home from the right kind of veggies," he adds.

Dirty dozen

According to a 2012 study from Stanford, organic produce has a 30 per cent lower risk of pesticide contamination, but is expensive. Scientists suggest that there is no need to spend on organic vegetables if you follow the vegetable washing technique. Some environmental groups advise avoiding juicing the dirty dozen - vegetables and fruits likely to contain the maximum amount of pesticides. The dirty dozen includes apple, celery, cherry tomatoes, cucumber, grapes, hot peppers, peach, potato, spinach, strawberry, sweet bell pepper and kale. Instead, choose asparagus, cabbage, cantaloupe, sweet corn, eggplant, mushroom, onion, papaya, sweet peas and sweet potatoes to juice.

It is best if you turn a vegetable into a smoothie - that includes the fibre - rather that juice. Fibre keeps you full for longer and is good for digestion. It also lowers cholesterol, helps maintain weight and stabilises blood sugar. If you prefer juice, add ground flax or chia seeds to it for the same benefits.

Dos and don’ts

• Avoid shiny or large vegetables
• Wash the veggies in running water
• Soak them in a tub of water to which a quarter cup of vinegar and a quarter teaspoon of sea salt have been added. Alternatively, you can use veggie wash
• Throw the water away and rinse the veggies in running water 2-3 times
• Cut off parts with signs of rot 
• Peel the vegetables carefully

The writer has a PhD in Inorganic Chemistry and is a hospital administrator