February 13th, 2014 by Digestive Detective
From the days of the Jack LaLanne Juicer to today's detox craze, juicing has been promoted as a marvel of nutritional therapy. While proponents highlight its natural goodness and ability to provide enzymes and concentrated nutrients, there are several considerations to make when choosing to add juicing to your nutritional repertoire.
Fructose to Fat
Juicing fruits and certain vegetables ensures that a high level of fructose will be present in the finished product. Part of the reason that high-fructose corn syrup garners so much attention for being problematic in the diet as a potential contributor to obesity is due to it's high concentration of fructose.
Fructose is absorbed and metabolized differently than glucose, the primary energy source for the body. With fructose, specific transporters, called GLUT5 transporters, allow fructose to enter intestinal cells. Fructose is then transported into the liver for storage. The metabolic pathway for fructose results in the formation of triglycerides through a process called de novo lipogenesis ("generation of new fat").
Additionally, because fructose functions and metabolizes differently from glucose, it does not trigger insulin response in the same way. Studies have shown that consuming fructose decreases insulin sensitivity. Decreased insulin sensitivity results in less ability to metabolize and get glucose into our cells and is one of the precursors to obesity, pre-diabetes, and diabetes.
The metabolic activity of fructose also prevents the activation of the hormone leptin. Leptin helps regulate appetite, thus this lack of leptin signaling from ingested fructose will simply leave you feeling hungry and unsatiated. Adding insult to injury, the elevated triglycerides created by high fructose consumption have been shown to impair the transport of leptin across the blood brain barrier meaning your brain won't receive the message that you are full when eating. Continual high fructose consumption thereby contributes to not only insulin resistance, but leptin resistance as well. When insulin and leptin are not functioning and responding properly in the body, deranged metabolism occurs resulting in weight gain and a viscous cycle of hunger and poor blood sugar management.
Oxalates & Mineral Absorption
Fructose isn't the only potential issue with juicing diets. Mineral inhibitors called oxalates are found in a variety of vegetables. Just as with eating fructose derived from whole fruits, consuming moderate to high levels of vegetables is not the problem. Vegetables are highly nutritious but when consumed in massive, concentrated amounts through juicing, the oxalates can pose a problem. Oxalates bind to minerals such as calcium and iron, preventing their absorption. So while a juice may be packed with minerals, several of those minerals may not actually be getting adequately absorbed into the body. Even greater caution should be taken by individuals with a history of kidney stones or any kidney dysfunction/disease as excessive intake of oxalates can result in calcium oxalate crystal deposits in the kidneys - a condition known as renal oxalosis. Researchers conducting a case review of the Mayo Clinic examined patients who were juicing and identified the heavy consumption of oxalate-rich juices as a potential cause of oxalate nephropathy and acute renal failure.
How to Juice Properly
In order to avoid these potential pitfalls with juicing, follow these steps:
- Instead of purely juicing, include the skins, rinds, and peels. These outer components of the fruits and vegetables will provide beneficial fiber that aids digestion, feeds healthy gut bacteria, and slows the absorption of the sugars from the fruits and vegetables, ensuring more even blood sugar response.
- Include some healthy fat. Adding a tablespoon of healthy fat such as coconut oil will also slow the absorptive rate of the carbohydrates, and will provide a vehicle for the absorption of important fat-soluble vitamins such as A, D, E, and K.
- Do not juice fruits alone. Blend vegetables with your fruits or stick primarily with vegetables for your juices. When juiced alone, fruits will spike blood sugar and if high in fructose, will lead to the effects mentioned above.
What are your experiences with juicing? Do you have any favorite combinations? Share below and join the discussion.