With the rise in popularity of intermittent fasting, a lot of people are beginning to question the traditional schedule of about five hours between meals. Conventional medicine still holds that waiting too long between meals can lead to negative effects on energy and metabolism. But emerging research claims the opposite — that eating all your meals inside a brief window can actually improve energy, weight management and overall health.
Some people need to eat several small meals a day, while others can go 12 or 16 hours without eating. There are benefits to both eating schedules, but it's ultimately a personal choice.
The Case for Regular Meals
Food is basically energy for your body. All the food you eat provides units of energy called calories that the body uses to support physiological function, like breathing and digestion, as well as your daily activities of living and any exercise you may do. Therefore, it makes a lot of sense to consume a diet with regularly spaced meals — for example, five hours between meals — offering a steady supply of energy.
Most mainstream medical experts recommend a regular meal schedule for the greatest health benefits. Skipping meals can cause low blood sugar, which can lead to poor cognition, confusion, irritability and fatigue, says Piedmont Healthcare Clinical Dietitian Haley Robinson. The body also ups production of the stress hormone cortisol, which you've probably experienced if you've ever felt "hangry."
Robinson also reports that skipping meals can cause a metabolism slump. Basically, when your body isn't sure when it's getting its next meal, it goes into "survival mode," slowing down metabolism to conserve energy. It also causes food cravings, overeating and poor food choice, Robinson says.
Read more: PROs and CONs of the 10 Most Popular Diets
The Skinny on Intermittent Fasting
Humans have been fasting for religious and cultural reasons for thousands of years, but it's become popular in mainstream culture only in the last decade or so. Intermittent fasting as a dietary regimen involves cycling through periods of restricted food intake and periods of unrestricted intake. The length and frequency of these cycles vary. Some people choose to fast for one entire day once or twice a week, others fast on alternate days and others fast for a designated time period each day.
Anecdotally, people who adhere to this dietary regimen claim it gives them sharper focus, helps them reduce their calorie intake for weight loss, revs their metabolism, helps them take their focus off food, helps with chronic medical conditions, boosts their energy levels and saves them time and money. Some of these are highly subjective benefits, yet others are beginning to be scientifically investigated. Although the research is nascent, there is some evidence that this dietary pattern can do what its proponents claim.
Intermittent fasting is particularly popular as an eating time table for weight loss. According to a systematic review of research published in the journal Cureus in July 2018, such restriction of daily food intake leads to significant weight loss results. In the four studies that met the review criteria, the effects were consistent among normal weight, overweight and obese subjects. The researchers concluded that, while more research is needed, intermittent fasting is a potentially powerful intervention for the obesity epidemic.
However, another study published in The American Journal of Clinical Nutrition in November 2018 specifically examined the intermittent fasting regimen known as "5:2" and found no weight loss benefit over a traditional calorie-controlled diet. At the end of the 50-week randomized, controlled trial involving 150 overweight and obese participants, there was no difference in weight loss between a group that ate an unrestricted diet five days a week and a 75 percent reduced-calorie diet two days a week versus a group that ate a daily diet with a 20-percent energy deficit.
As for its other health benefits, a July 2017 review in the Annual Review of Nutrition analyzed results from 18 studies and concluded that intermittent fasting may have positive effects on the following biological and physiological systems that influence metabolic regulation and the development of obesity, diabetes, cardiovascular disease and cancer:
- Circadian biology: Restricting energy intake in the evening hours synchronizes with circadian rhythms and optimal post-meal hormone response. This may lead to improved circadian rhythms and better regulated energy metabolism and body weight.
- Gut microbiota: Time-restricted feeding may contribute to a healthy diversity of gut microflora, which impacts metabolic health.
- Lifestyle behaviors: Intermittent fasting may reduce energy intake and improve energy expenditure as well as sleep quality. Eating late at night has been associated with poor sleep quality, which can increase the risk of obesity and chronic illness.
Read more: 13 DOs and DON'TS of Intermittent Fasting
Choosing Your Meal Schedule
The most important thing is to make sure you're getting enough calories and the correct amount of nutrients to support good health. Nutrient deficiencies from not eating enough, or eating only specific foods, can lead to fatigue, shortness of breath, dizziness, pale skin, irregular heartbeat, muscle weakness and more. In addition, it's crucial to make sure you're not getting too many calories, especially those from unhealthy foods. Part of the effectiveness of intermittent fasting may be the emphasis on consuming healthy, whole foods during meals.
As long as you are eating a healthy diet, how long to wait between meals might be more of a personal preference and a decision based on how you feel when you go too long without eating. Some people are more sensitive to skipping meals than others; for those individuals, eating regular meals — and potentially more frequent, smaller meals — may be the best choice.
If your goal is weight loss, the best diet is one that is sustainable long term. While intermittent fasting might work for a little while, it can be a difficult regimen to maintain when the demands of work, family and personal life get in the way. Intermittent fasting is akin to a lot of fad diets that are very restrictive in caloric intake or consumption of certain foods, and the Academy of Nutrition and Dietetics advises staying away from these diets.
Yet, there are many proponents who swear by intermittent fasting, and that might be enough to convince you to jump on the bandwagon — at least to see if it's for you. There's no reason why you shouldn't give it a try, as long as you keep a few things in mind:
- If you have a medical condition, be sure to get the go-ahead from your doctor before choosing such an eating plan. According to the American Osteopathic Association, certain populations should use caution when considering intermittent fasting, including pregnant women, people with a history of eating disorders, women without a menstrual cycle or hormone regulation issues, people at risk of hypoglycemia and people who are very active in their job or exercise activities.
- Start slowly, perhaps restricting calorie intake between the reasonable hours of 7 a.m. and 7 p.m. If that seems to pose no problem for you, you can try abbreviating the window gradually over time.
- Focus on healthy foods including lean meat and fish, whole grains, fruits and vegetables, moderate amounts of dairy, healthy oils and nuts and seeds.
- Plan your meals carefully to make sure you are getting enough of the right macronutrients — protein, carbs and fats. Planning ahead also ensures that you don't fall off the bandwagon and reach for processed, nutrient-deficient snack foods that will leave you feeling hungry — or hangry — again soon after eating.
- Piedmont Healthcare: "What Happens to the Body When You Skip Meals?"
- Harvard T.H. Chan: "Diet Review: Intermittent Fasting for Weight Loss"
- Cureus: "Intermittent Fasting: The Choice for a Healthier Lifestyle"
- The American Journal of Clinical Nutrition: "Effects of Intermittent and Continuous Calorie Restriction on Body Weight and Metabolism Over 50 Wk: A Randomized Controlled Trial"
- Annual Review of Nutrition: "Metabolic Effects of Intermittent Fasting"
- Mayo Clinic: "Vitamin Deficiency Anemia"
- Academy of Nutrition and Dietetics: "Staying Away from Fad Diets"
- American Osteopathic Association: "Intermittent Fasting: Can We Fast Our Way to Better Health?"