Consuming blended drinks has been shown by studies to lead to higher availability of antioxidants and other chemicals in the plant food item than is possible with juicing; dietary concentration of polyphenols has been shown to be inversely proportional to chronic disease.
Two randomized controlled studies on the effects of consuming commercial fruit and vegetable puree drinks following both acute and chronic consumption show that despite increases in dietary ascorbic acid levels pureed drinks did not alter levels of ascorbic acid in blood plasma. Antioxidant and oxidative stress levels were not altered with any significance.
Juice cleansing is not the same as juice fasting, it is a different process concerned with detoxifying the body via limiting consumption of foods to that of only fruit or vegetable juices for a period of 3-10 days while fasting from solid foods. More aggressive juice fasting is commercially available and typically lasts only for one day.
Juicing increases bioavailability of vitamin C, flavonoids, and other phytochemicals. When more than 5 fruits or vegetables are consumed in juice form over an eight hour period or longer dietary and plasma phytochemical, antioxidant, and micronutrient activity are increased.
Juice fasting causes changes in body metabolism, initially LDL levels will increase but will decrease as triglycerides are mobilized to supply energy to the body, cholesterol reduction lasts for about a week after fasting. Semi-starvation state may occur from prolonged and acute fasting, which stimulates the body to conserve its fat stores and inhibit activity. Vitamin C prevents endothelial injury due to lipid peroxidation, and promotes fatty acid oxidation by moving long chain fatty acids across the mitochondrial membrane. Honey which is typically added to juice drinks lowers blood lipid levels as well. All this together may help to prevent inflammatory, cardiovascular, neoplastic and neurologic processes if maintained for a long period of time. Lack of nutritional balance precludes this diet use as a long term sustainability measure.
Fruits and vegetables are high in fermentable fiber, conferring prebiotic activity on them. Reduced risk of cardiovascular disease, some cancers, and type 2 diabetes are associated with high fiber diets. Oligosaccharide fiber substrates for intestinal microbes produce energy and other beneficial compounds including short chain fatty acids.
Purred juices lack fiber and contain a lot of glucose, which leads to stronger feelings of hunger as blood sugar levels spike and drop, which can lead to weight gain. Blood sugar level spikes and drops manifest in brief spurts of energy followed by slumps, tiredness, irritability, headaches, stiffening of red cell membrane hindering passage through body increasing cholesterol deposits. Hypertriglyceridemia and hyperglycemia can result from fasting too long or too often.
Excess fiber in blended drinks can be problematic as well leading to excessive intestinal bloating, gas, and abdominal cramps. Drinking sufficient amounts of water is important when on a blended vegetable and fruit diet to help avoid these issues and to help with proper stool formation.
Lack of protein may result in protein deficiency which can escalate if the juice diet is prolonged, added a protein powder supplement is recommended to avoid this issue. Sometimes nut milk is added to a juice diet as well to compensate for some of the missing amino acids. Many studies have shown lack of protein leads to a feeling of not being full, creating want to eat more, which is another drawback of this kind of diet, giving added pressure to that temptation to eat something rich and filling to struggle with. Lean muscle mass is lost when there is a protein deficit, which means all weight lost will be regained. Weight loss is primarily due to water loss and does not have longevity if not done in combination of more sustainable healthy eating habits.
Juice fasting basic cons are limited nutrient availability, high sugar intake, and loss of lean muscle mass. Basic pros are consumption of puree based foods and drinks are a great way to add these nutrients into a diet that will help to promote overall cardiovascular health.
