Research needed to determine success of time-restricted eating

Nutrition and fasting

Dear Doctors: My sister and I have gotten serious about reaching a healthy weight. We are following the Mediterranean diet, and we’re walking 2 miles each day. We have both lost weight, but she’s losing faster. The only difference is she says she’s doing time-restricted eating. What is that?

Dear Reader: Congratulations to you and your sister for making positive lifestyle changes. Walking and the Mediterranean diet have each been shown to play a role in good health and improved well-being.

When it comes to your sister losing weight more rapidly, a number of factors may be at play. Time-restricted eating may be the most obvious variation in your two approaches to your weight-loss goals, but it isn’t necessarily the definitive one. Additional factors that can affect weight loss include differences in your metabolic rates, blood sugar metabolism, disordered sleep patterns, medical conditions, medications, tobacco and alcohol use, general activity levels, genetics, disparities in the composition and preparation of your meals and accuracy in how you each calculate your total food intake.

Time-restricted eating, sometimes referred to as daily intermittent fasting, is a strategy in which someone eats only during a set number of hours each day. The specific schedule of eating and fasting depends on each person’s needs and preferences. Someone may decide to eat during a six-, eight- or 10-hour window each day. The rest of the time, they abstain from food. Most people set aside at least 12 consecutive hours during which they consume no food at all. They do drink water to stay hydrated, and may also include noncaloric beverages.

Studies into time-restricted eating produce mixed results. Some have found it can help with weight loss. Whether this is due to metabolic changes or because limited time to eat favors lower caloric intake wasn’t clear.

Other research has looked at symptoms of metabolic syndrome. This is a cluster of conditions that, when they occur together, raise someone’s risk of Type 2 diabetes, heart disease and stroke. The conditions that contribute to metabolic syndrome are excess abdominal fat, high blood pressure, high blood triglycerides, low levels of LDL (so-called “good” cholesterol) and high blood sugar. Three or more of these factors qualifies someone as having metabolic syndrome. In those studies, time-restricted eating helped to reduce the risk factors for developing metabolic syndrome.

Elizabeth Ko, MD and Eve Glazier, MD

On the minus side, a large study published in the journal JAMA Internal Medicine found the practice of daily intermittent fasting could lead to reduction in muscle mass.

At this time, there is no conclusive evidence that time-restricted eating spurs faster weight loss. Studies into the strategy have either been short and with few participants, or they have used animal models. Because the topic is fairly new, long-term studies into the potential positive or negative outcomes of the approach are also not available. We continue to counsel our patients to eat from a wide range of foods, with a focus on lean proteins, healthful fats and plenty of fresh fruits, leafy greens and vegetables. We think your plan of following the Mediterranean diet, along with regular daily exercise, is a good one. Stick to it, and we believe you will see results.

(Send your questions to [email protected], or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)