Intermittent fasting

How it works: There are two common approaches to fasting: One is to eat very few calories on certain days, then eat normally the rest of the time. The other involves eating only during certain hours, and skipping meals for the rest of each day.

What it promises: Even with free eating periods, fasters tend to take in fewer calories overall, resulting in weight loss. In addition, advocates believe that intentionally depriving your cells of calories may slow the progression of certain age-related diseases.

The upsides: Some people find it easier to have bulletproof willpower for just part of the time than to eat more moderately all of the time. Several small studies have found lower blood sugar, blood pressure and cholesterol levels with fasting.

The downsides: Larger, long-term studies are still lacking, so most of the proposed benefits are theoretical or based on animal research.

Mayo's verdict: There's simply not enough research (yet) to support or debunk this trend, and shortening your eating window may make it difficult to get the vitamins and minerals you need. Athletes especially may find it difficult to fuel and refuel appropriately for an active lifestyle.