This Dietitian's Honest Thoughts About Time-Restricted Eating and Intermittent Fasting
Not a week goes by where I’m asked my opinion on intermittent fasting. Hands down, intermittent fasting (IF) has been one of the top dieting trends of the last decade. Tell me you don’t know someone doing it….
In this article, I share my thoughts as a Dietitian and Health Expert on the benefits, pros and cons, and science behind intermittent fasting.
What is Intermittent Fasting?
For those who don’t have their office buddy to tell them all about their IF protocol that’s working wonders for them, let’s briefly define intermittent fasting.
Intermittent fasting involves cycling between periods of fasting and eating, essentially creating patterns or “cycles of fasting”.
What’s unique about it, is that rather than a typical diet that focuses on WHAT to eat, intermittent fasting focuses on telling you WHEN to eat.
There are several forms of intermittent fasting:
24-Hour Fast: No eating for a 24-hour period, once or twice per week. On other days, eat as normal.
Alternate Day Fasting: Every other day, consume around 500 calories, or 25% calories less your regular, healthy diet.
Twice-a-Week Method: Restrict calories to 500 total on two days of the week. On the other days, eat as normal.
Time-Restricted Eating: Eat within a restricted time or “eating window” each day.
The form of IF I will focus on today is the most popular, and the most simple form for those new to fasting to implement, that is Time-restricted Eating.
Let’s Explain Time Restricted Eating
Time restricted eating is a type of intermittent fasting that limits your food intake to a certain number of hours each day.
The two most popular methods include:
16:8 Method: Eat within an 8 hour window (ie. 10am -6 pm), and fast (aka do not eat) the other 16 hours.
14:10 Method: Eat within a 10 hour window, and fast the remaining 14 hours. .
Time restricted eating has increased in popularity in recent years as a way to lose weight and boost metabolic health by simply condensing one’s eating hours into a defined interval of time.
What’s the reasoning behind it? In the past, humans did not have access to food 24/7 as most of us do now. Today, we can pretty much eat whatever we want, whenever we want. Some have argued that eating excessively around the clock (without properly fasting like our ancestors did) leads to disruption of our circadian rhythm, possibly contributing to obesity and metabolic diseases (ie. heart disease, diabetes) over time.
From this came the trend of time-restricted eating and intermittent fasting to help “reset” the circadian rhythm with the hopes of extending lifespan, and for many, with the hopes of losing some weight in the process.
Lets take a closer look at the benefits and drawbacks…
Advantages / Possible Benefits of Intermittent Fasting
Let’s review the potential advantages and benefits of intermittent fasting based on recent research.
WEIGHT LOSS
This is what I see as the BIGGEST draw to intermittent fasting/ time restricted eating.
Anecdotally, I have heard from several of my clients that intermittent fasting did assist in modest weight loss after a few weeks of following it consistently.
Looking at the research however, certain studies have reported significant weight loss but other studies have found no result.
The question is whether changes are due to the body using and burning fat cells more efficiently as a result of fasting, or if the weight loss occurs due to calorie restriction. The answer is unclear, and likely it is a combination of both.
Simply put, having less time to eat in the day means less time to consume calories Limiting food intake to only certain number of hours in the day can help individuals naturally consume less calories without having to strictly calorie count.
Some research has also shown that eating in a smaller window may help reduce levels of the appetite-stimulating hormone ghrelin in the body. Less hunger may lead to less calories being consumed (which yes, can lead to weight loss overtime).
However, the weight loss benefits of intermittent fasting may be more than just calorie restriction due to a shorter eating interval. Studies have shown that intermittent fasting in rodents may help the body preferentially burn ectopic fat and alter lipid metabolism. In other words, the body would prefer to burn fat tissue during a fasted state. However, there haven’t been many studies conducted in humans, and it’s unclear whether this effect is sustained long term.
CARDIOVASCULAR HEALTH & LIPID PROFILES
Several studies have shown that fasting (specifically time restricted eating) may help improve heart health by improving lipid profiles (triglycerides, cholesterol levels) if followed for an extended period of time.
A study done in healthy males practicing fasting for Ramadan showed a significant decrease in LDL-cholesterol (“bad” cholesterol) and increase in HDL-cholesterol (“good” cholesterol) after one month of fasting when compared with levels prior to their fasting.
What’s the mechanism? During the fasting window, glucose levels in the body are low, and ketone levels increase. When this occurs, the body does something called “intermittent metabolic switching” and switches to using ketones for energy instead of glucose. The body essentially becomes more efficient at utilizing energy from adipose (fat) cell tissue at this point, and these metabolic changes to lipid use may result in the weight loss and improvements in lipid parameters that have been seen with intermittent fasting.
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GLYCEMIC CONTROL & BLOOD SUGARS
For those with blood sugar control issues (pre-diabetes, type 2 diabetes), intermittent fasting and time restricted eating is gaining popularity as an adjunctive treatment method and potential alternative to medications.
There is some evidence that patterns of fasting can help improve insulin sensitivity. The idea is that the fasting period would essentially give the cells a chance to rest from constantly being bombarded with glucose, and help to increase their sensitivity to sugars over time by allowing more sugar to enter the cell, instead of build up in the blood which occurs with type 2 and pre-diabetes. In turn, this could help to reverse or prevent type 2 and pre-diabetes.
However, some studies have shown that intermittent fasting is no more effective that continuous calorie restriction for blood sugar markers.
I have seen clients who were able to reduce their blood sugar levels into a normal range by following an intermittent / time restricted feeding protocol for several months. However, the results were likely not just attributed to their change in eating time and frequency, as they also made adjustments to HOW they were eating within their feeding window.
This being said, it is important to consider the amount and types of foods being consumed within the eating window. For optimal blood sugar management, one should make sure to still space out their carbohydrate intake, choose nutrient and fiber dense whole foods such as complex starchy vegetables and fruits most often, and limit processed and refined carbs to support a more balanced blood sugar profile.
As a whole, the research on diabetes and IF is minimal and inconclusive at this point, and we still have much more to learn.
MINDFUL EATING
For those that eat around the clock and graze without any real structure to their eating, switching to a time-restricted eating pattern may help them to become more aware of their food choices and enjoy the food when they consume it.
The impact of shortening the eating window can help some individuals become more attune to their natural hunger cues. Simply being more in touch with our sensations of hunger and fullness can help us become more mindful of our timing, amounts and choices of foods. We also tend to enjoy our food more when we are actually hungry!
Disadvantages of Intermittent Fasting
Let’s review the potential disadvantages and drawbacks of intermittent fasting based on recent research.
QUESTION OF THE SUSTAINABILITY OF FASTING
Like any positive change made to diet or implementing a new habit, consistency is crucial. Finding the type of protocol you’d like to try out (such as time-restricted eating) and try that out for at least a few weeks consistently, is necessary to see any sort of change or results.
However, with IF, the act of eating within a short time period during the day may be hard for some people to stick to long term. What happens if you are travelling? Your family is in town for the week? Will you shift your eating patterns to accomodate? This is something to consider in terms of your ability to be consistent with it.
For those that thrive on routine, time restricted eating can offer a stable framework for timing of meals/snacks. This can help with a daily structure for those who struggle with planning, choosing and preparing their foods on a daily basis due to busy schedules. For example, knowing that breakfast will always be at 10am, lunch at 1pm and dinner at 6pm can help them stay on track with eating regular meals and balanced portions.
FASTING MAY NOT BE SUITABLE FOR DIFFERENT POPULATION GROUPS
Competitive athletes who train for a significant number of hours in their day or week have VERY high energy (aka calorie) needs. Simply put, they may not be able to consume enough food to support their training in a 6 or 8 hour window. This could set them up for increased risk of injury, overtraining syndrome, illness, and even hormone imbalances.
This could also include pregnant and breast feeding women whose main priority is to make sure they are intaking enough nutrition to support a growing baby.
For those with diabetes on insulin or other blood-sugar lowering medications, IF should only be done under the supervision of an experience clinician. The same should be said about those on medications that require food to work properly.
What to Consider if You’re Considering Intermittent Fasting
Considering intermitting fasting? Here’s what you need to keep in mind.
PLANNING FOOD INTAKE AROUND WORKOUTS WHEN FASTING
An issue I see a lot is that people are doing their activities / workouts / exercise in a time outside their eating window. This means that pre/post workout nutrition is overlooked, and might be negatively impacting recovery and progress.
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CONSISTENCY WITH FASTING IS KEY
Only following the protocol Monday-Friday then binge-eating on the weekends probably won’t get you the results you are looking for. IF is a big lifestyle change; it takes commitment and consistency to see changes occur.
CHOOSING YOUR FASTING EATING WINDOW
You will need to consider your lifestyle – if you want to eat dinner with your family, then this will likely mean you have a later eating frame.
If you find an 8 hour window to be too extreme, you could experiment with a longer eating interval (10-12 hours) to consume your food within, or choose to not eat 3-5 hours before bed which may also have benefits.
The Takeaway
In summary, by limiting your calorie intake to a specific time interval, you may see benefits including weight loss and metabolic health. However, much of the research that is currently out is inconclusive, so don’t believe the claims that time-restricted eating can fix everything.
Personally, I try to eat within a 10-hour window each day and feel best when I do so. I avoid eating very early in the morning, waiting until I’m hungry to eat my first meal or snack (usually around 10am). I avoid eating late in the evening so that my sleep and digestion are not impacted.
Like any dietary pattern, what’s important is to assess your lifestyle and goals and find what works for YOU. For those with higher calorie and nutrition needs, time restricted eating may require a lot of preparation and might not be suitable. For those who require a structure, it might be the answer.
However, if other avenues have not yet been addressed (diet quality, sleep, exercise, stress management), then using intermittent fasting as the first measure to improve your health probably isn’t the best idea.
If you have tried other measures though, and nothing seems to be helping, there may be benefit in trying intermittent fasting. However, I would suggest working with a dietitian who can help you plan out your meals and snacks to ensure you are meeting your needs, monitor your progress, and help make the program sustainable for your lifestyle.
For more fitness, metabolism and wellness tips, be sure to follow along with me on instagram at leighmerotto_rd.
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