Q: Do "detox" diets that make you fast for the first few days have any health or weight-loss benefits? —Dinah, Salt Lake City

A: Detox diets often require drinking only water and fruit and vegetable juice for the first three to seven days. This supposedly cleanses your system of toxins to produce mental alertness and increased energy. But detox diets do not help with long-term weight loss. Although some people do lose weight during the first few days of a fast, it isn't fat loss — it's primarily just water weight that comes right back once you start eating again.

And detox diets can be dangerous. Fasting can cause drastic fluctuations in electrolytes (compounds in the blood that regulate your heartbeat and other muscles) and blood sugar levels. Such fluctuations can cause heartbeat irregularity and dips in energy levels that can lead to headaches, dizziness and, potentially, coma. Fasting is particularly dangerous for people with diabetes or heart and kidney problems, as well as pregnant and nursing women, the elderly and children, because their bodies are more likely to react negatively to electrolyte and blood sugar changes.

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So, overall, detox diets aren't especially healthy. But many detox plans do have a few grains of wisdom that you can incorporate into your current diet:

Hydrate. A key principle of most detox plans is drinking plenty of water. The Institute of Medicine recommends that women drink about nine glasses (72 ounces) each day. Water is essential for all body functions, such as regulating body temperature, eliminating wastes and delivering healthy nutrients and oxygen to our cells.

Eat more produce. Detox diets emphasize eating fruits and vegetables. The United States Department of Agriculture (USDA) recommends that we eat 2 cups of fruit and 2.5 cups of vegetables each day.

Choose fewer processed foods. Detox diets promote eating natural, whole foods, because processed foods are usually high in calories, sugar and fat and low in nutrients. Processed foods such as ice cream, soft drinks, doughnuts, chips and cookies can be difficult for most of us to cut out completely, so aim to eat them in moderation — about 150 calories' worth or less each day.

The bottom line? Fasting is not healthy, and we don't need special diets to detox, because our bodies have a natural detoxification system: The liver, kidney, lungs and skin are constantly ridding our bodies of toxins and waste from the environment such as household cleaners, food additives, drugs and pollution. A better approach to getting healthy and losing weight permanently is a good old-fashioned low-calorie, balanced diet and regular exercise.

Dawn Jackson Blatner is a registered and licensed dietitian, and a national media spokesperson for the American Dietetic Association. Read more about her here.