Does intermittent fasting work for weight loss?

Clock on a plate

Intermittent fasting is a type of diet that has caught a lot of attention recently because it focuses on when you eat rather than what you eat. Some people have found this strategy to be more helpful long term than focusing on the specific foods they eat. But does it work for long-term weight loss? See what an endocrinologist says about this trendy diet.

What is intermittent fasting?

Fasting is abstaining from food for a specific period of time. Basically, if we fast for long enough, our body switches from using mostly glucose (sugar) to mainly using fat-derived substances for fuel. This will also happen if you burn significantly more calories than you eat by restricting calories overall. Using stored body fat as an energy source helps you lose weight. 

Two popular fasting regimens include:

  • Restricting the number of daily hours you eat (also called time-restricted eating). The 16/8 method is fasting each day for 16 hours and eating all your calories within eight hours. For example, you may choose to only eat between 10 a.m. and 6 p.m.
  • Restricting the total daily intake of calories on specific days. 5:2 intermittent fasting is where you would eat normally for five days of the week but significantly restrict calories for the other two days

Brianna Johnson-Rabbett, MD, is an endocrinologist who works with people who want to lose weight. She says, "There is some data that fasting results in changes in metabolic pathways that could have positive effects on health separate from effects on weight, though this is still an area of active research. However, there's no reliable evidence that fasting regimens result in more weight loss long term than daily calorie restriction."

Intermittent fasting can help with weight loss, as long as you're eating less overall than you would normally. This type of diet can be a useful tool if it works with your lifestyle, habits, preferences and overall health.

How to start intermittent fasting

If you've never fasted before, it takes some getting used to. Here are some tips to help you get started:

  1. Talk to your doctor. Some medications don't mix well with fasting. For example, fasting while taking the sulfonylurea class of diabetes medications can be dangerous, as fasting can significantly increase the risk of low blood sugars. Certain other medications must be taken with food to be absorbed properly. People with cancer, or people on many medications (like older people can be) usually shouldn't fast. Talk to your doctor before starting to fast as she or he may recommend against it or need to adjust certain medications before you start fasting
  2. Get the right nutrients. While trying to lose weight, make sure to eat lots of vegetables and lean protein. This combination can maintain nutrition and help you feel full longer. Limit simple sugars and simple carbohydrates like sweets, pop, and white bread
  3. Watch out for symptoms. Some people have symptoms such as headaches, mood changes, decreased energy levels or constipation when they start fasting. These symptoms may resolve over time as your body gets used to your new schedule. However, not everyone can tolerate fasting well and generally any significant symptoms should result in cessation of a fast
  4. Start small. A simple way to start fasting would be to not eat anything after supper (unless for medical reasons). After establishing that as a regular habit, you can start eating breakfast later and later until you can skip it or combine it with lunch

If you aren't hungry in the morning, eating breakfast isn't necessary (unless you need to for medical reasons). Dr. Johnson-Rabbett says, "Forcing intake of breakfast has not been demonstrated to be a reliable weight-loss strategy".

Be sure to talk to your doctor before you begin a new weight-loss strategy, especially if you have chronic health conditions.

Dr. Johnson-Rabbett also notes, "Snacking in between meals or eating six small meals a day usually doesn't support weight loss, so I don't recommend it for most adults unless needed for a specific medical condition. Interestingly, the increasing rates of excess weight in the United States population are closely mirrored by the introduction and marketing of snacks in our society, though correlation doesn't equal causation."  

If you need a little help reaching your weight-loss goals, the Bariatrics Center is the most comprehensive weight management program in the region. The program was designed and directed by physicians who are specialty trained in medical weight management.

To schedule a free information session, please call us at 402.559.9500.