There’s been a lot of buzz about intermittent fasting lately, but it’s time to turn to the science to answer: “What is intermittent fasting for weight loss?” I’ll also share a plan and tips to get started with intermittent fasting, if you decide it is right for you.
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Formats of Intermittent Fasting for Weight Loss
Intermittent fasting means intentionally not eating during certain time periods, in order to give your body a break from active digestive and metabolic processes. The most common formats of intermittent fasting are called time-restricted eating and 5:2 fasting.
Time-restricted eating refers to setting a daily eating window and a fasting window. The typical format is to fast for 16 hours and theneat for 8 hours during the day (called a 16/8 fasting schedule). For example, a person may choose to eat their meals between 11 am-7 pm, then fast until 11 am the next morning. Other common windows are 14/10 and 18/6.
5:2 fasting occurs across a week, rather than each day. This approach involves eating your typical calorie intake for 5 days of the week and then significantly reducing your calories to 500 per day for 2 days of the week.
The Benefits of Intermittent Fasting for Weight Loss
There has been a lot of scientific interest in the past 5 years for how intermittent fasting approaches may help with weight loss. One of the most attractive ideas behind this approach is that you focus on changing when you’re eating more than what you’re eating. But, the focus on when to eat can incidentally also help people change what they eat. For instance, you might turn down late-night snacks because they are now outside your eating window. Or, you may pick higher protein foods because they make it easier to meet your fasting window.
So, what does the science say about intermittent fasting for weight loss?
A recent review by Freire (2020) looked at the findings from 7 studies where research participants were put on intermittent fasting eating plans for 4 to 24 weeks. On average, participants lost between 4-10% of their body weight during the research studies lasting between 1-6 months (meaning a total of 8-20 pounds if their starting weight was 200 pounds). This is a promising rate of weight loss.
Notably, the rates of weight loss appear to be similar to continuous calorie restriction— like the common approach of reducing calories to 1200-1500 per day, every day. In support, research studies comparing intermittent fasting to continuous calorie restriction have found no significant differences in rates of weight loss over similar time periods (Rynders et al., 2019; Stockman et al., 2018).
This is good news. These findings suggest that focusing on when you eat also improves what you eat. Ultimately, you can decide whether it is easier for you to hit your calorie target for weight loss using an intermittent fasting approach, compared to the typical calorie restriction approach.
Health Benefits of Intermittent Fasting
In addition to the benefits of intermittent fasting for weight loss, there are also ways that intermittent fasting can improve your health.
Freire (2020) reported that the benefits of intermittent fasting across 6 in humans included:
- Improved insulin sensitivity
- Decreased body fat
- Reduced blood pressure
- Reduced glucose (blood sugar) levels
- Decreased lipid (like triglycerides) levels
- Reduced inflammation
In 6 studies of animals, Freire (2020) noted that additional benefits of intermittent fasting included:
- Reduced rates of cancer, type 2 diabetes, and cardiovascular (heart) disease
- Reduced signs of aging and up to a 30% longer life span
According to Mishra & Singh (2020), these benefits are thought to occur because periods of fasting give your body time to:
- Engage in resting metabolic processes related to fat burning
- Clean waste from your cells and replace damaged cells (a process called autophagy)
- Activate molecular and genetic expression related to longevity and disease prevention
Overall, the research shows that while intermittent fasting and continuous caloric restriction may lead to similar outcomes for weight loss, intermittent fasting may have unique benefits for physical health.
Who Should Not Intermittent Fast?
I would not recommend any type of fasting or calorie restriction plan for any individual who has a history of an eating disorder or is experiencing any current symptoms of disordered eating. These symptoms can include: episodes where eating feels out of control (binge eating), vomiting or using laxatives/diuretics for the purpose of weight loss, constant thoughts about food, weight, or body shape, excessive exercise (2+ hours per day), or severe calorie restriction (<1000 calories per day). For individuals with disordered eating, intermittent fasting may trigger feeling of restriction related to food consumption and/or binge eating episodes.
Please also speak with your healthcare providers before starting an intermittent fasting plan if you have diabetes. Going for long periods of time without eating may cause your blood glucose (blood sugar) to decrease to a hypoglycemic level.
In addition, talk with your healthcare providers before beginning intermittent fasting if you take medications that in the morning that need to be taken with food.
How to Start Intermittent Fasting for Weight Loss
The key to starting to intermittent fast is to take it slow. Your body is currently biologically adapted to your current pattern of eating. So, you want to give yourself time to adjust to a new eating schedule.
Personally, I recommend time-restricted eating over the 5:2 format, because it is less restrictive and may have higher rates of adherence. Simply adjusting your eating window is a bit easier to do than picking two days of the week where you’re eating only 500 calories.
Sample Intermittent Fasting Plan
Here is an example of how you can work up to the typical 16/8 (16 hours fasting, 8 hours eating) schedule over the course of a month. Let’s pretend that the person’s typical eating window was between 7 am to 11 pm (16 hours eating, 8 hours fasting).
- In month 1: reduce eating window to 7am thru 9pm (14 hours eating, 10 hours fasting)
- Next, in month 2: reduce eating window to 8am thru 8pm (12 hours eating, 12 hours fasting)
- Then, in month 3: reduce eating window to 9am thru 7pm (10 hours eating, 14 hours fasting)
- Finaly, in month 4: reduce eating window to 11am thru 7pm (8 hours eating, 16 hours fasting)
If you’re feeling anxious to dive in 100%, try to remember that your body needs to adjust. You don’t want to spike your stress hormones by making such a significant change that your body thinks it is in danger of starving. Stress can increase fat storage and prevent weight loss. Building new, sustainable habits takes time. You deserve to approach intermittent fasting in a way that is kind to your body. Easing into this new pattern makes it more likely that you’ll stick to it long-term and see all the benefits described above. In contrast, making a change too quickly can trigger you to say “this is too hard” and give up. Do it right, and make it last.
Tips for Intermittent Fasting
You may be interested in learning more about the science and benefits of intermittent fasting. If so, I encourage you to read The Obesity Code by Jason Fung, MD. Dr. Fung also shares some amazing tips for making intermittent fasting feel easier (a.k.a. more likely you’ll stick to it long enough to see the benefits!).
Some of the top tips reflected in The Obesity Code, research studies, and my patient (and personal!) experience are:
Prioritize high-protein meals and snacks during your eating window.
Protein is the most important macronutrient for satiety and satisfaction from your meals. For fasting, this means that the food you eat is more likely to tie you over until your next eating window.
Break your fast with a combination of protein and fat.
You want to avoid spiking your blood glucose (sugar) right when you break your fast. Instead, eat a meal that is high in protein and fat, such as two eggs with 1/4 avocado on an OuterAisle cauliflower sandwich thin (the everything bagel seasoned one is incredible!).
In a pinch, you can start by breaking your fast with one of these nutrient-dense pre-made protein shakes or protein powders. I personally recommend the products from Orgain, and you can try their grass-fed whey or premium vegan protein powders with a buy one, get one FREE deal right now!
Know what you can eat/drink while in a fasting window.
Water and zero-calorie beverages are encouraged in abundance while you are fasting. I personally recommend staying away from beverages with artificial sweeteners (like splenda/sucralose and aspartame). Unsweetened sparking waters are the best choice– Bubly is my favorite!
Good news for caffeine lovers– black coffee and tea can be enjoyed during fasting windows! Just don’t add any milk/cream or sugar.
Four Sigmatic is a coffee brand that contains ingredients specifically formulated to promote mental clarity, including mushrooms and lion’s mane. Many fasting enthusiasts love it.
Herbal teas can also support your fasting efforts. For example, this herbal tea by Pique is formulated to support your immune system and gut health, which can set you up for success to reap the benefits from your fasting windows.
Support your gut health with probiotics.
Having good bacteria in your gut can amplify the benefits of intermittent fasting, according to Dr. Fung, author of The Obesity Code.
One of the most rigorously tested probiotics on the market is by Klaire Labs. This supplement has 25 billion units of probiotics and has been specially formulated in a base on prebiotic inulin fiber. Klaire Labs created this project without any additives and cannot be broken down by stomach acid, so it will only be absorbed in your digestive tract where it belongs.
Listen to your body.
There may be days when you wake up feeling starving and fatigued. Learn to listen to your body and perhaps decide not to practice intermittent fasting on those days. You don’t have to intermittent fast every single day to enjoy its benefits. If you find yourself struggling to follow through with intermittent fasting often, consider reducing your fasting window or changing the types of foods you eat during your eating window (hint: more protein!).
Dr. Schulte’s Summary
Intermittent fasting involves either restricting the number of hours you eat each day or reducing the number of calories you eat on certain days throughout the week. Intermittent fasting has been found to result in similar amounts of weight loss as consistent calorie-controlled programs. This suggests that focusing on when you eat can have benefits for improving what you eat. In addition, intermittent fasting has been associated with an array of benefits to physical health, such as better glucose control, reduced blood pressure, and decreased risks for type 2 diabetes and heart disease.
What has your experience with intermittent fasting been like if you have tried it?
Freire, R. (2020). Scientific evidence of diets for weight loss: Different macronutrient composition, intermittent fasting, and popular diets. Nutrition, 69, 110549.
Mishra, S., & Singh, B. (2020). Intermittent Fasting and Metabolic Switching: A Brief Overview. Biomedical and Pharmacology Journal, 13(3), 1555-1562.
Rynders, C. A., Thomas, E. A., Zaman, A., Pan, Z., Catenacci, V. A., & Melanson, E. L. (2019). Effectiveness of intermittent fasting and time-restricted feeding compared to continuous energy restriction for weight loss. Nutrients, 11(10), 2442.
Stockman, M. C., Thomas, D., Burke, J., & Apovian, C. M. (2018). Intermittent fasting: is the wait worth the weight?. Current obesity reports, 7(2), 172-185.
Disclaimer: all opinions are my own and are not affiliated with my employers. Please seek medical guidance before pursuing weight loss or making significant changes to the way you eat or your physical activity routine.