Almost daily I have a conversation with a client who is attempting to eat three small meals plus three small snacks per day. This person is often struggling to lose weight and also happens to never really be hungry. The only reason this individual is eating so frequently is because someone told her to.

In stark contrast to the six-small-meals-diet is an increasing popular eating pattern called Intermittent Fasting. So what exactly is the science behind not eating?

What is Fasting?

Fasting, put simply, is a period of time during which an individual abstains from food and drink. For weight loss purposes, two methods of fasting have been proposed as an alternative to the traditional continuous calorie restriction: time-restricted fasting and alternate day fasting.

Here are a few definitions to help you out:

Continuous Calorie Restriction (CCR): The “traditional” way to lose weight, which is essentially to estimate a person’s calorie needs and then subtract a portion to limit the daily intake of a person. For example, for a person who needs 2,000 calories per day, limiting daily intake to 1,500 calories will yield about one pound of weight loss per week.

Time-Restricted Fasting (TRF): An eating pattern in which a person fasts for a set period of time during a 24 hour day. Different durations of fasting times have been proposed, from eight hours in a day up to 21 hours. Some of these eating patterns limit meals to one per day; others divide the meals up to 3 per day (6, 7).

Alternate Day Fasting (ADF): An eating pattern in which a person eats ad libitum (as much as you want) on 4-5 days of the week and fasts (either completely or limiting to 20-25% of calorie needs) on the other 2-3 days of the week (1, 6, 9, 10). This eating pattern has been popularized by The 5:2 Diet Book.

A Brief History of the Fasting Diet

Many world religions encourage or require periods of fasting: periodic fasting in the Church of the Latter Day Saints; time-restricted eating patterns of Seventh Day Adventists; and the holy month of Ramadan in Islam during which participants fast from sun-up to sun-down.

Observational studies of these groups of people have been correlated with a variety of health benefits including lower weight, lower fasting glucose, lower cholesterol, and fewer incidences of diabetes (4, 6, 7). These observations have spurred researchers to ask how TRF and ADF affect human metabolism and weight.

How Intermittent Fasting Works

The benefits of intermittent fasting are not fully known, but there are several mechanisms by which ADF and TRF may work better than traditional calorie restriction.

Circadian Rhythm

Circadian rhythm – i.e. having a regular sleep schedule based on daylight – appears to be important for optimal metabolic function. Research from animal studies shows a strong link between circadian rhythm and regulation of hormones and metabolism including improvements in body weight, lipids, glucose, insulin, and inflammatory markers. (6, 7).

Data from human studies in this area is limited, but the deleterious effects of shift-work and poor sleep patterns are well-known. Nighttime eating has also been associated with poor sleep quality and reduced sleep duration (7).

Normal circadian rhythms may also benefit the gut microbiota (those happy little bacteria in your colon), but this research has largely been studied in mice and needs future research in human subjects to further understanding (6,7).

Long-Term Lifestyle Behaviors

Continuous calorie restriction seems simple enough. Indeed, this type of restriction is effective… when people actually follow the calorie restriction. Dieters often regain weight when returning to old habits after stopping the calorie restriction (which is why support as you’re making changes is so important!) (9, 10).

Rather than thinking about “dieting” all of the time, fasting allows the individual to take a “break” from dieting and eat what they want on feed days; thus there is possible improvement to the adherence of this eating pattern in the long-term (1, 10). However, some studies have shown a higher dropout rate for participants following ADF than participants following CCR, indicating dissatisfaction with the diet (9). There isn’t a one-size-fits all eating pattern.

Contrary to popular belief, studies have shown that periods of fasting do not necessarily lead to overeating on non-fasting days or meals (1, 4, 6). Some studies have shown slightly more consumption on non-fasting days, but because followers of this eating pattern eat much less on fasting days, the net calorie consumed is still 35-40% less than their typical diet which yields initial weight loss and then weight maintenance over time (1, 7, 10).

Basically, a person can incorporate aspects of fasting at any point to help get back on track with weight loss or moderate overall calorie consumption if he knows he’s overeaten on other days.

Preservation of Lean Mass

A common argument for the six-small-meals-per-day argument is to maintain a high metabolism. The theory is if a person goes too long without eating, the body will go into “starvation mode.” However, a preliminary study comparing ADF and CCR showed no difference in resting metabolic rate (the amount of calories you burn at rest) (3). Other studies show ADF is as effective as CCR in terms of weight loss and visceral fat mass while possibly preserving muscle mass (1, 5, 10).

As for TRF, the old adage that “breakfast is the most important meal of the day” may not be true (read more about the science of breakfast). Some studies have shown that skipping breakfast does not necessarily cause overeating at lunch and can even help with weight loss (6). A randomized controlled study in athletes showed benefits of TRF during resistance training, with participants in the experimental group showing improvements in lipids and reduced fat mass, while maintaining muscle mass (5).

Indeed there is truth that as a person loses weight he burns fewer calories, but this does not necessarily appear to be related to the timing of food intake or the duration of food restriction.  Any type of weight loss will inherently mean your body burns fewer calories. Even if the only weight lost was from fat, a person’s calorie needs (metabolism) would still go down.

The reduced metabolism with weight loss appears mostly to be related to the decreased energy expended for physical activity. If a person loses 50 pounds, it’s like he just stopped carrying around a 50 pound backpack. If you’ve ever gone backpacking, you know it takes a lot of energy (calories) to lug the big backpack around. Once you take off, you just don’t need to eat as much to keep yourself going (8).

Improved Metabolic Profile

Improvements in lab values (lipids, glucose, insulin levels, ets.) are correlated with reduction of body weight and visceral fat; it’s unclear if it is the specific fasting patterns of ADF and TRF that improve lab values or if it is the overall reduction of weight which improves these outcomes. Several studies show improvements in lab values with CCR as well as ADF, but ADF is not necessarily better (1, 2, 3, 4).

In one study of time-restricted feeding, participants consumed similar calorie amounts – but either consumed these all in one meal or divided the calories into three meals. The results showed decreased fasting glucose and improvements in LDL and HDL cholesterol for the group which consumed all calories in one meal and fasted the remainder of the day (7). However, more research needs to be done before outlining specific fasting recommendations.

Precautions to Take with Intermittent Fasting

Any kind of calorie restriction – whether CCR or intermittent fasting – can reduce need for certain types of medication such as blood-glucose lowering drugs for diabetes (2). The unique calorie intake variations of fasting may require day-to-day adjustments in specific medications, so always talk to your healthcare provider before starting a diet.

There are also still a lot of questions science has yet to answer about fasting – for example, what length of time is ideal to fast? How much calorie restriction is necessary on “fasting” days? How many days per week should a person fast?

No surprise, but the biggest complaint when following a fasting diet is hunger, irritability, feeling cold, and having low energy (so maybe warn your significant other about possible “hanger” symptoms before you try this). However, study participants also report improvements in mood overall, including reduced tension and anger, less fatigue, and improved self-confidence (3, 4, 6, 7).

In addition, this diet may not be right for someone with a history or propensity towards restrictive forms of disordered eating. Everybody has a right to fuel his body well and too many days of “fasting” may not be healthy (4).

Intermittent Fasting: Overall Grade

Weight balance: Grade A

Maintenance: Grade B

Traditionally, CCR has been the method to force the body to use stored energy (i.e. fat) to lose weight. In contrast, new studies show equal weight loss with ADF and TRF as CCR, but may show benefits in long-term adherence to these eating patterns (1, 7).

The major benefit to these types of eating patterns is that they are very straightforward. There is no calorie counting. No restrictions on what type of food to eat. No measuring of foods. No saying “no” to your cravings – at least on your feed days. Both of these eating patterns focus on timing of meals rather than what a person eats (1).

Nobody eats perfectly all the time, so an eating pattern which allows for more food choices and normal variance in intake of calories may lend itself to improvements in long-term adherence.

Personally, I incorporate many aspects of intermittent fasting into my eating routine – and I’ve done so for a long time without knowing or naming it (take a look at my eating pattern). I stop eating after dinner in the evening so I wake up Hungry (with a capital H) and ready to break my overnight fast – thus practicing TRF. There are some (rare) days when I’m not hungry in the morning or when I just don’t have time to eat lunch. On these days I might only eat half of my normal calorie needs – an example of ADF.

My point is – intermittent fasting can be used as a tool to help you learn to listen to your body’s hunger cues. I give this diet a high maintenance grade because you can pick it up whenever you need to. Just take a day and take a break from all the cookies in the break room at work. Use your lunch break to go on a walk and drink a can of sparkling water in the afternoon to curb your hunger. I downgraded the maintenance grade from “A” to “B” because Hanger is real, people, and I don’t want it to destroy your relationships.

But fasting might not be for you. If you’ve struggled with disordered eating or tend to be overly restrictive, this might not be a healthy choice. Everybody (and every body) is different.

If you want to talk about it more in person, book a discovery call and let’s talk about your nutrition needs. Whatever you choose, I hope you’ll be happy, be healthy, and choose something delicious to break your fast.

With love from Peas and Hoppiness.

Want help with your nutrition?

Sources

1. Alhamdan, B. A., et al. “Alternate-Day versus Daily Energy Restriction Diets: Which Is More Effective for Weight Loss? A Systematic Review and Meta-Analysis.” Obesity Science & Practice, vol. 2, no. 3, 12 June 2016, pp. 293–302., doi:10.1002/osp4.52.

2. Carter, Sharayah, et al. “Effect of Intermittent Compared With Continuous Energy Restricted Diet on Glycemic Control in Patients With Type 2 Diabetes.” JAMA Network Open, vol. 1, no. 3, 20 July 2018, doi:10.1001/jamanetworkopen.2018.0756.

3. Heilbronn, Leonie K, et al. “Alternate-Day Fasting in Nonobese Subjects: Effects on Body Weight, Body Composition, and Energy Metabolism.” The American Journal of Clinical Nutrition, vol. 81, no. 1, Jan. 2005, pp. 69–73., doi:10.1093/ajcn/81.1.69.

4. Horne, Benjamin D, et al. “Health Effects of Intermittent Fasting: Hormesis or Harm? A Systematic Review.” The American Journal of Clinical Nutrition, vol. 102, no. 2, Jan. 2015, pp. 464–470., doi:10.3945/ajcn.115.109553.

5. Moro, Tatiana, et al. “Effects of Eight Weeks of Time-Restricted Feeding (16/8) on Basal Metabolism, Maximal Strength, Body Composition, Inflammation, and Cardiovascular Risk Factors in Resistance-Trained Males.” Journal of Translational Medicine, vol. 14, no. 1, 2016, doi:10.1186/s12967-016-1044-0.

6. Patterson, Ruth E., and Dorothy D. Sears. “Metabolic Effects of Intermittent Fasting.” Annual Review of Nutrition, vol. 37, no. 1, 2017, pp. 371–393., doi:10.1146/annurev-nutr-071816-064634.

7. Patterson, Ruth E., et al. “Intermittent Fasting and Human Metabolic Health.” Journal of the Academy of Nutrition and Dietetics, vol. 115, no. 8, Aug. 2015, pp. 1203–1212., doi:10.1016/j.jand.2015.02.018.

8. Rosenbaum, M, and R L Leibel. “Adaptive Thermogenesis in Humans.” International Journal of Obesity, vol. 34, no. S1, 2010, pp. S47–S55., doi:10.1038/ijo.2010.184.

9. Trepanowski, John F., et al. “Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults.” JAMA Internal Medicine, vol. 177, no. 7, 1 May 2017, doi:10.1001/jamainternmed.2017.0936.

10. Varady, K. A. “Intermittent versus Daily Calorie Restriction: Which Diet Regimen Is More Effective for Weight Loss?” Obesity Reviews, vol. 12, no. 7, 29 Jan. 2011, pp. e593–e601., doi:10.1111/j.1467-789x.2011.00873.x.