Vegetable and fruit juice based diets are growing in popularity among busy people who don’t have the time to get in their daily fruits and veggies. Fruits and vegetables are sources of many biologically active things that help health and decrease the risk of disease.  For example fruits and veggies have molecules called polyphenols.
Polyphenols have a variety effects that have been proven in the lab such as being antioxidants, immune system stimulating, and killing bacteria.  Polyphenols are not well absorbed by the body and often continue to the colon where they can be digested by bacteria in the gut. These bacteria break down polyphenols into smaller molecules which also become food to other bacteria. Fruits and vegetables are also high in fermentable fibers which have prebiotic activities. Prebiotics are compounds that bacteria living in us, can use as food to grow. High fiber intake has many positive effects like lowered risks of cardiovascular disease, type 2 diabetes, and some cancers. 
The gut microbes play a role in our everyday health. One of these roles is that the gut microbiota has been shown to affect the development of obesity and obesity-related disease.  The two types of bacteria which are found in humans in greatest numbers are the Firmicutes and Bacteriodetes.  Studies have shown that supplementing diets with more polyphenols shows a decreased amount of Firmicutes and more Bacteriodetes. This is interesting because lowered Firmicutes levels and higher Bacteriodetes is also associated with leaner individuals, while obese people have opposite proportions.  A scientific study followed a 3-day juice-based diet of 6 blends of fruit/vegetable juices. The results showed that people lost significant amounts of weight and kept it off for two weeks. People on this diet showed increased amounts of Bacteroides bacteria which can degrade plant fibers and complex polysaccharides. 
What fruits/veggies are high in polyphenols?
The break down: Research shows that leaner people have the same gut bacteria, that the juice diet promotes. Although this may not mean instant weight loss, studies are showing that the juice diet has definite benefits to the body. Why not add more juice to your diet?
Rule of thumb: Choose fruits and veggies that are richly hued when juicing. For example, red and purple fruits often are excellent sources of polyphenols. However, don’t be afraid to stray to other colours. All fruits and veggies have nutrients and vitamins that are good for your bodies.
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