Juice Fast Diets and Weight Loss: Science Behind the Results

Detox diets typically consist of periods of extreme fasting and are sometimes coupled with exercise. The diet, it is often claimed, helps to remove accumulated toxins from your body and leaves you feeling refreshed, invigorated, and often a few pounds lighter.

Detox diets have recently gained increased attention due to the popularity of the feature-length documentary “Fat, Sick, and Nearly Dead.” This film (written, directed, and starring Joe Cross), chronicles his inspirational weight-loss story as he uses a juice-fast to meet his weight loss goals and recover from an autoimmune disease called urticaria. The transformational journey captured in this film is truly remarkable, but it also raises a question as to whether there is sufficient scientific evidence to support a juice-cleanse diet for the majority of people.

The use of a detox diet, specifically juicing, usually results in an initial period of rapid weight loss. A person undergoing this first phase of juicing almost certainly has a significant calorie deficit which partially contributes to their weight loss. However, there is another potential explanation for this accelerated weight loss.

Humans consume vitamins and minerals in our diet every day. In particular, we consume quite a bit of sodium through food intake on a Western diet. In fact, the average American diet may consist of 3.2 g of sodium per day, and 90% of this sodium comes from processed, added sodium. Normally, a person’s kidneys work to balance the amount of sodium consumed versus the amount of sodium excreted. In doing so, the kidneys control something called “plasma osmolality” within a very tight range. Osmolality is a term which describes the amount of a substance dissolved per mass of its solvent. In other words, a high salt concentration results in a high molality. (Note: molality is affected by more than just salt in animals)

Our kidneys are very well-evolved machines that can adapt nicely to changes in our diet. However, the extreme changes associated with juice diets are too quick for our kidneys to properly adjust in the first few days of the diet. Your kidneys will be getting rid of too much sodium because you’re taking in much less sodium than you were only a few days before. To account for this imbalance, your body responds by secreting less of a protein called vasopressin (or anti-diuretic hormone). Normally, vasopressin causes your body to retain water. When a person is on a juice fast, though, the body needs to excrete more water to balance out the reduced intake of sodium.

The increased excretion of water through urine can explain the rapid weight loss associated with the beginning of juice-cleanse diets. Even when a person diets by simply eating less of a standard western diet, their sodium intake is decreased because total food intake is reduced, and water excretion increases. And while it may still be true that some of the weight loss is due to fat loss, the vast majority of weight loss during the first week of a juice cleanse is likely to be water weight.

Any diet which claims to be a “detox” diet is walking on very thin ice scientifically. There is a little, if any, evidence to support the notion that extreme diets or fasting can help expel toxins. Most toxins are rapidly and effectively removed from the body via urine and feces, and it’s unlikely that a juice diet does anything to affect that. (although constipation may very well be a side effect). However, there are some potential positive health effects of juicing in addition to weight loss.

Several peer-reviewed publications have indicated that juices and some fruit extracts may exert protective effects due to their antioxidant potential. Multiple animal models have shown that juices can reduce inflammatory markers, and, in some models, reduce the extent of atherosclerosis which is the major cause of most heart attacks. Most recently, a randomized clinical trial in humans showed that immune health was improved when subjects drank Concord grape juice versus a placebo.

Some juices have been also been shown to have a positive effect on blood pressure regulation. In human patients, consumption of pomegranate juice has been observed to slightly lower systolic blood pressure. As an added benefit, pomegranate juice also seems to lower the plasma levels of a protein called ACE, which is a risk factor for atherosclerosis.

Given this preliminary evidence, further research should be done to understand how juice diets may affect cardiovascular health. To be clear, though, most of the beneficial effects of juicing are purely speculative at this point, and you should be skeptical of anyone who promises dramatic results from a week-long diet.

Juice fasts have gained traction due to recent publicity. For most people, juice diets are more than likely to be a safe challenge. However, an individual should still be aware of possible complications. They include:

• Fatigue
• Dehydration
• Nausea
• Constipation
• Headache

Fatigue and dehydration may occur due to excessive water loss during the first part of the diet.

The evidence to support clear health benefits of a completely juice-based diet in humans is lacking. Instead, why not consider integrating antioxidant rich juices into a balanced diet that also contains whole grains, nuts, dairy products, and lean meats? Any potential health benefits from juice can surely be gained from a balanced diet without the need for an extreme fasting regimen that is a component of the most popular “cleanses” today.

As always, before you begin a diet or workout routine, you should talk to your physician to make sure you are healthy enough to begin. Whatever you decide, good luck to you, and I hope you find health and stay healthy.