Updated December 16, 2014.

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.
There are a lot of potential benefits to reduced-carbohydrate diets. Some of them have been intensely studied, while others have been commonly reported among people who have reduced the carbohydrate in their diets. Not everyone will gain all these benefits, of course. People who are more sensitive to carbohydrates (insulin resistant, metabolic syndrome, prediabetic, etc.) are likely to receive the most benefit.

 

Scientifically Demonstrated

Although I have linked to only one study for each of these claims, there are many studies, often going back decades, that show similar results. This is why I feel safe in saying these results have been demonstrated. However, note that in many of these studies, people were not screened for factors such as insulin resistance. If the group most likely to benefit is studied, rather than a random sample, the results could be stronger.

• Weight loss (even when not consciously restricting calories)
• Improved triglycerides
• Reduced blood glucose for diabetics and pre-diabetics
• Increased HDL (“good”) cholesterol
• Improved insulin sensitivity
• Decreased blood pressure
• Lower blood insulin level
• Compared to high-carb weight loss diets (and when combined with exercise), less muscle mass lost
• Ketogenic diets (one type of low carb diet) used to treat seizure disorders

Preliminary Evidence

Some studies have shown these benefits from carbohydrate reduction, but more study is needed before a definitive statement can be made.

• Improvements in acne
• Improvements in Polycystic Ovarian Syndrome
• Improvements in Irritable Bowel Syndrome

Commonly Reported

These are some of the most commonly reported benefits in low carb forums, support groups, and informal surveys. (Some have preliminary scientific evidence, but more subjective improvements are harder to study.) The first two are by far the most commonly reported, and these benefits usually happen by the end of the first week, although sometimes it takes another week or two. Results are obviously going to be variable between individuals.

• Increased energy
• Less heartburn
• Cravings for sweets gone or dramatically reduced
• Better mental concentration; no “brain fog”
• Improved mood; emotions more even
• ”Compulsive” or “emotional” eating gone
• Improved dental hygiene (less dental plaque; improved gum health)

Sometimes Reported

These are more variable, partly dependent upon the symptoms the person was having in the first place. Again, a low carb diet can in no way be considered a cure for these conditions, and this is not a scientific survey. Also, rest assured I am not listing every benefit I have ever heard of - these have been mentioned enough to make me think that there is validity to them for some people.

• Improvement in joint or muscle pain
• Fewer headaches
• PMS improved
• Reduced intestinal gas
• Improvement in skin appearance