Curious about intermittent fasting? Read this science-backed guide to learn more and get a free 7-day intermittent fasting diet plan PDF. Updated May 8, 2023
So many different diets claim to help with disease prevention and weight loss: low-fat, low-carb, ketogenic, DASH, paleo, vegetarian, vegan, Mediterranean, MIND, etc. But I want to talk about one of the latest trends: intermittent fasting.
You may be used to eating three meals every day, plus snacks. That’s pretty common. With intermittent fasting, you can eat how much of whatever you want—but here’s the catch: you must stay on schedule. So there are scheduled periods of time when you can eat and others when you fast with intermittent fasting.
Unlike most other diets, intermittent fasting tells you when to eat, not what to eat. And, many people say that it can help lead you to better health and a longer life. Sound interesting? Let’s do a deep dive into intermittent fasting 101.
Most weight-loss diets work by reducing the number of calories consumed. Intermittent fasting does the same thing but in a different way. This way of eating limits calories (requiring fasting) for certain durations of time (intermittently) while allowing few or no restrictions the rest of the time.
Thus, in a nutshell, intermittent fasting essentially means skipping meals regularly, sometimes daily, weekly, or even monthly. Here are a few popular approaches to intermittent fasting 101:
Probably the most popular method of intermittent fasting. With 16:8 IF, you fast for 16 hours and then eat for 8 hours in a day. Many people choose this method as it is one of the easiest and simplest to follow.
Most people who do the 16:8 split skip breakfast and break their fast around lunchtime. For example, they would have their first meal at around 11 am and eat until 7 pm that night, creating an 8-hour eating window. Other people may choose any earlier eating window, such as 8 am-4 pm.
Consuming regular meals for five days per week, then restricting to no more than 600 calories per day for the other two days (typically non-consecutive). This happens by eating very little and drinking only water or non-caloric beverages on those two fasting days.
Eating normally one day but only a minimal amount of calories the next, alternating between “feast” days and “fast” days every other day.
With periodic fasting, you restrict calories for several consecutive days and eat unrestricted meals on all other days. For example, fasting for five straight days per month.
In addition to these types of intermittent fasting, another approach, The Prolon Fasting Mimicking Diet (FMD), is gaining popularity for helping to prevent disease and promote weight loss.
Studies show that intermittent fasting can achieve weight loss. However, the success is similar to other diets. So, yes, similar—not necessarily better.
Overall, research on the effect of intermittent fasting on people’s health is still emerging as to whether it can also prevent disease or slow down aging in addition to some weight loss for some people.
Most of the research on calorie restriction and intermittent fasting has been conducted in cells (e.g., yeasts), rodents, and even monkeys. Some, but not all, of these studies, show fasting may help build exercise endurance, enhance immune function, and promote longevity. It also seems to help reduce disease risk for diabetes, heart disease, certain cancers, and Alzheimer’s.
When it comes to clinical studies (those done in people) on intermittent fasting, most have been pretty short—a few months or less. But, we know so far that it may help with markers of inflammation (C-reactive protein), diabetes (blood glucose levels and insulin resistance), fat burning/fat loss, and help reduce high blood pressure and cholesterol.
When it comes to weight loss, intermittent fasting seems to work just as well—not better—than other diets. Researchers think that eating this way decreases appetite for some people. With a smaller appetite, you eat less, which will help you lose weight.
What about extending the lifespan of humans? Those studies haven’t been done yet, so we don’t know the effects of intermittent fasting on our lifespan.
When we don’t eat enough calories, we use up stored carbohydrates called glycogen. The liver stores enough glycogen to last 12 to 16 hours before running out of fuel. Beyond 16 hours, the body switches fuels and begins using fat as an energy source.
At this time, metabolism shifts from a carbohydrate-burning to a fat-burning state. Some of the fat is used directly as fuel, while some is metabolized into biochemicals called ketones. The state of ketosis brings other changes throughout the body that are thought to underlie some of the health benefits seen with some types of fasting.
Ketones are a more efficient energy source for our bodies than glucose, so they keep many of our cells working, even during periods of fasting. This is particularly true for brain cells and may be part of the reason some animal studies show protection against age-related declines like Alzheimer’s.
Ketones may also help ward off some cancers and inflammatory diseases like arthritis. They are also thought to reduce the amount of insulin in the blood, which may help protect against type 2 diabetes.
On a molecular level, intermittent fasting may extend lifespan in animals because of its effect on genetic DNA. It appears that, in animals, restricting calories may slow down these age-related changes and help them live longer.
All of this being said, most people who follow a 16:8 intermittent fasting diet plan don’t get into ketosis. Thus, weight loss benefits are mostly attributed to decreased calorie intake, and overall health benefits may be attributed to decreased blood sugar and insulin levels.
Bottom line: Stay tuned for more research to understand better the effect of intermittent fasting on health and aging.
As with all major dietary changes, be sure to discuss intermittent fasting with your healthcare professional or book a consultation with me. I’d love to work with you!
If you want to try an intermittent fasting diet plan, the first step is determining if you’re a good candidate. Next, please consult with your physician before trying intermittent fasting if any of these conditions apply to you: Pregnant or breastfeeding, diabetes or hypoglycemia, low blood pressure, eating disorder (or history of), underweight, amenorrhea, or trying to conceive, take certain medications (i.e., diuretics for high blood pressure), and/or if you’re under 18.
Next, decide WHY you want to try intermittent fasting and write down your health goals. Some reasons may include improved blood sugar levels, manage insulin resistance, weight loss, or healthy aging.
Monitor for potential side effects when starting intermittent fasting. These may include fatigue, weakness, headache, reductions in sexual interest, and a reduced ability to maintain body temperature in cold environments. Many of these side effects are temporary, but if they last longer than a week or two, consider stopping intermittent fasting for a while and see if your symptoms improve.
It’s also important to assess whether intermittent fasting is helping you achieve your health goals or not. Consider starting a journal, at least initially, to use on your intermittent fasting journey. Things to monitor might include mood, energy level, blood sugar, blood pressure, and weight (I recommend waist measurements instead of weighing yourself as a way to monitor fat loss). This will help you decide if intermittent fasting is a good health strategy for you in the long run.
The main reason for any dietary change is to have a sustainable and healthy lifestyle that helps you meet your health goals. Whether you’re looking to lose weight or prevent disease, intermittent fasting is one eating style that may work for you.
The most important thing with any diet is to get all of your essential macro and micronutrients, appropriate amounts of food, and fiber for a healthy gut microbiome and enjoy your lifestyle in the long run.
Any diet or eating pattern that helps some people may not have the same effect on everyone. That’s why it’s important not to make any significant dietary changes without consulting your healthcare professional or dietitian.
If you want to start intermittent fasting, book an appointment with me to see if my program/service can help you. And, as a bonus, I’m offering a free 1-week 16:8 Intermittent Fasting Meal Plan Printable PDF to my newsletter subscribers!
While some research suggests an earlier eating window (i.e., 8a-4p) is best for weight loss, you can still improve health parameters and lose weight with a later eating window, such as 11-7. Ideally, eating your last meal 2-3 hours before bed would be best. Bottom line: Choose an eating window that best suits your lifestyle and that you can stick to in the long term. You may need to do a little experimentation to see what that is.
Is intermittent fasting safe for people with diabetes?As mentioned above, if you have diabetes (type 1 or 2), you should consult your physician before trying intermittent fasting. One tiny study looked at 3 men who had type 2 diabetes for 10-25 years. They did an alternate day or periodic fasting under medical supervision and were able to stop taking insulin after 1 month. In addition, they were able to reduce or stop medications after 1 year. Again, this is a small study. Please consult with your physician before trying intermittent fasting if you have diabetes.
How many calories should you eat on 5:2 fasting days?Most people who do 5:2 intermittent fasting consume about 500-600 calories 2 days per week and eat normally the other 5 days. If one of your goals is weight loss, depending on your caloric needs, this should support 0.5-1 pound of weight loss per week. If you do 5:2 fasting, it’s essential to ensure you eat high-fiber meals and adequate protein on non-fasting days.
What can you eat or drink while following an intermittent fasting diet plan?While fasting, water, unsweetened seltzer, tea, and black coffee are all permitted. Some intermittent fasting practitioners allow small amounts of cream, half-and-half, or milk in coffee. This is fine if you are using intermittent fasting as a way to decrease your overall calorie intake. If you are using intermittent fasting as a way to get into ketosis, keep in mind that even small amounts of caloric liquids may increase your blood sugar and insulin levels.
Does intermittent fasting slow your metabolism?Like many people, you may have read somewhere that it’s better to eat several mini-meals throughout the day to keep your metabolism up. While some people, especially those with GERD, gastroparesis, or other GI disorders, do better with frequent small meals, no good evidence supports many mini-meals to keep metabolism up.
Indeed frequent eating throughout the day may result in an overproduction of insulin to try and lower blood sugar. This may actually lead to weight gain in some individuals. However, as stated earlier, some studies have shown that lean muscle mass is more easily preserved with IF than with calorie-restricted diets and does not negatively affect metabolism as low-calorie diets do.
How can you prevent overeating at the end of the day?Focus your diet on eating mostly whole, minimally processed, high-fiber foods, including vegetables, fruit, beans/legumes, nuts, seeds, and unrefined grains. You may also include lean, high-quality animal protein (fish, poultry, wild game, grass-fed beef, eggs, & dairy) and healthy fats (i.e., avocado, extra virgin olive oil, expeller pressed high oleic sunflower oil,& nuts/seeds).
This will help keep you well-fueled and satisfied, making you less likely to eat after your eating window. If you are new to time-restricted feeding, start slowly. Try decreasing your feeding window by 30 minutes to –one hour every day or two until you find your optimal eating window.
I designed this 1-week Intermittent Fasting Diet Plan PDF to show you a healthy 16:8 meal plan. While you can adapt any “diet” to an intermittent fasting schedule, this plan features high fiber, low glycemic carbohydrates, lots of veggies and some fruit, healthy fats, and high-quality proteins to help keep you full, energized, and satisfied.
You will eat 3 meals/day over an 8-hour window. For example, I typically eat between 11a-7p; however, you can pick the 8-hour eating window that best suits your lifestyle.
The plan averages 1550 calories/day to promote 0.5-1 pound of weight loss per week. If you do not need/want to lose weight, you may add additional low-glycemic, high-fiber foods to each meal to increase your daily caloric intake.
If you are new to intermittent fasting, as mentioned earlier, I suggest keeping a food and mood journal for the first couple of weeks to monitor for any side effects (i.e., headaches, fatigue, hormonal imbalances, etc.) you may experience at the start of intermittent fasting.
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