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Time-Limited Eating Guide

Through the Calibrate program, you’ve learned a lot about what to eat. While following the Calibrate Food Triangle is very important, when you eat is another critical tool for improving weight and metabolic health. Limiting the period of time during which you eat can be a useful (and evidence-based) strategy, especially if you’re feeling stuck on the scale or are looking for ways to take your metabolic health to the next level. 

Adjusting the windows during when you do—and don’t—eat is often called intermittent fasting, but the approach we’re going to use here is a specific, pared-down version that we call “time-limited eating” (TLE). In a nutshell, you’ll be confining your eating to an 8 (or fewer) hour window. In this guide, we’ll cover how this technique works, and then how to implement it.

What’s happening within your body

From a practical standpoint, you can probably ascertain why shortening your eating window might give you more control of your food habits. When you have less time to snack and graze, you tend to eat less overall. But reducing your eating window goes well beyond how much you’re eating. By simply giving your body more time without the influx of food, you start to influence your biology in important ways.

Eating around the clock is a relatively new concept in human history (and therefore a new curveball for human biology). When people eat, insulin levels stay high. Not having much time with low insulin levels can contribute to weight gain—or resistance to weight loss—and other metabolic dysfunction (such as insulin resistance and diabetes).  A major advantage of limiting your eating window to no more than 8 hours is that you give yourself at least 16 hours for insulin levels to drop. 

When your insulin levels are low, you can break down fat and use it for fuel. During the first 12 hours of not eating, your body first utilizes glycogen, easy-access energy stored in the liver to maintain normal functions. But after a certain period of time (generally around 16 hours; the minimum amount of time we’re going to ask you to close the kitchen for (though it can take longer for some people), those energy stores become depleted. When this happens, your body has no choice but to find an alternate mechanism for energy production. 

That’s when you begin burning fat stores rather than carbohydrates, marking the beginning of a fat-powered energy state called ketosis. Your liver responds to the depletion of glucose and glycogen by converting fatty acids to ketone bodies, and these ketones provide steady, fat-derived energy. This gives your body a break from digestion and teaches it to use its own energy stores (the fat stores) more effectively—a process known as metabolic switching. As you burn fat, you’ll also lose weight.

Importantly, in forcing your body to use its own energy stores, you’re doing more than just burning fat- a good thing in itself. You are helping to increase insulin sensitivity; in fact, fasting has been shown in multiple studies (like this one and this one) to reverse insulin resistance in people with prediabetes or type 2 diabetes. Even beyond weight loss and insulin, you are also  activating pathways that may help enhance performance and slow aging and disease.

An intro to the 8/16 (or 6/18) approach

While there are several ways to go about time-limited eating (again, also commonly known as intermittent fasting or “time restricted feeding” in scientific studies), we’re going to ask you to carve out no more than 8 hours for food and leave at least a 16 hour window open for fasting. This isn’t as dramatic as it sounds because you’ll ideally be sleeping for 8 to 9 of those hours. In fact, you may not even realize it, but you’ve probably restricted your window to this ratio at some point in your life. If you’ve ever slept in late and delayed eating until lunch the following day, that probably amounts to at least 16 hours of fasting. 

If you really want to supercharge this technique, a 6/18 window may be even more effective. We realize that’s a big change for many, so we start with recommending 8/16, but know that if you’re up for the challenge, you can swap the numbers out below. 

While you can choose any eight hour period for your eating window, research does suggest that eating earlier in the day is preferable when it comes to optimizing the insulin response and metabolic health. An 8 AM breakfast generates less insulin than eating the exact same food as an 8PM dinner. In one study, eating dinner before 3 PM not only created sustained reductions in insulin and lower blood pressure,  but surprisingly, people in the restricted window felt less hungry than people who ate the exact same amount spread throughout the day. 

That said, we know eating dinner before 3 PM is tricky. If it’s doable for you, moving your last meal earlier in the day is preferable from a metabolic health perspective. But we want Calibrate to work for you not the other way around, and family dinners, socializing, and after work routines are important. If 9-5 or 10-6 works for you, those are good options, too. No matter which window you choose, make sure you are allowing your body at least three hours in between your last meal and bedtime for a more restful, deep sleep. 

The goal with TLE is to limit the time you're eating to at most eight hours, so all meals and snacks should occur within that time frame. Do not feel obligated to try to cram into 3 meals and 2 snacks per day; rather, listen to your hunger cues, find a rhythm that works for you, and consider the kitchen closed at all other times. To help ease yourself into this approach, try bumping your meal times by an hour each day until you get to the window you want. For example, if you normally have breakfast at 8 AM, move it to 9 AM on day one, 10 AM on day two, and so on. Do the same in reverse with evening meals if necessary. If you want some help managing your schedule, we love Zero, a free app for iPhone and Android. 

Lastly, pay attention to your body as you’re getting used to TLE (we’ll bring it up again later in the guide, but this is definitely a good time to lean on a photo journal, like the one you used in your Level 1 Emotional Health class). While this amount of time without food should not cause symptoms, if you are on insulin, it’s worth keeping an eye on your sugars (you may not need as much insulin given the positive changes we described above). If you begin to feel unwell, it’s OK to eat something, and you can reach out to the medical team about suggestions for how to approach TLE in a way that will work for you. 

Tips for success

Like any other health practice, TLE gets easier the more you do it. Here are a few tips to help you as you kick things off.

  • Most people find the first week or so to be the hardest, so hang in there if the first few days are challenging! As you make the change to a reduced eating window, you may be hyper-aware of what time it is, how much you’ve eaten, and what else you have time to eat. You may even think you hear your stomach growling louder than normal. The physical and psychological effects (including fears of going hungry) are common in those just starting out TLE. Remember your eating with mindfulness skills, and you may even want to use a food journal for a week or two. 
  • Stay hydrated throughout the day, inside and outside of your eating window. It’s important to avoid falling short on fluids to help with digestion and detoxification. Hydration also fights off hunger, boredom, and fatigue. One other tip on the hydration front (and good news!): black coffee and tea are not just OK, they may also make the “fasting” time easier and help with the metabolic benefits. Importantly, do not add sugar or milk to your tea/coffee outside of your 8 hour window, as this will disrupt the benefits of your food-free window.
  • Look to the Calibrate Food Triangle to deal with the physical sensations that are challenging you, i.e. the actual hunger. For your 8-hour eating window, make sure you’re consuming the foods and food combinations you’ve been learning about throughout the program. Focus on filling combinations of protein, fiber, and healthy fats to keep you feeling satiated throughout your eating window and beyond. 
  • Keep an eye on grocery shopping. Now more than ever you’ll want to avoid red foods like processed foods and artificial sweeteners, as these products will throw your appetite, fullness, and hunger cues and cravings off balance. Similarly, in the early days, stock your kitchen with only the amount of food you’ll actually need during your new eating window. If you know your eating window won’t include a classic breakfast, there’s no need to buy breakfast food for the house. And if there are any treats you know having on hand will tempt you to snack at night or in the other off-hours of your limited window, refrain from buying them and stocking them in your pantry or freezer.
  • Be mindful about overeating during your 8-hour window. Know that you can follow the triangle, listen to hunger cues, and you will have the time with (and without) food that your body needs to be healthy.  To help you along, try to maintain some kind of food schedule (the Zero app can help with this), and (we can’t stress this enough) don’t feel like you have to stick to 3 meals and 2 snacks. The number of “meals” is up to you and your hunger level that particular day. Another helpful tip here is to avoid over-exercising before your window starts (which can lead to overeating) or eating more carbs in your later meals (since they’ll drop your blood sugar and leave you hungrier). Know that if you give your body the fuel it needs, you don’t need to worry about being hungry or overdoing it on your final meal (instead, keep listening to your regular hunger/satiety cues).

A few more reasons to feel good about TLE

Aside from weight loss and improved metabolic health, fasting and limiting eating windows have been shown to reduce inflammation, allowing the body to rest, recover, and initiate important cellular repair processes without the intrusion of constant feeding and digestion. Body inflammation can contribute to various chronic conditions and autoimmune diseases, and fasting has been shown to be beneficial for patients with arthritis in slowing disease progression.

Brain function also benefits from periods of fasting. When in the fasting state, the body produces brain chemicals that support increased learning and memory and may be connected to slowing progression of neurodegenerative disorders like Alzheimer’s and Parkinson’s.

And then there’s longevity. Time-restricted eating may help you live longer; its longevity-linked benefits include improved markers for cardiovascular health like blood pressure, resting heart rate, and good cholesterol, as well as enhanced ability to inhibit growth and multiplication of cancer cells and change expression of certain genes.

Time Limited Eating is yet another valuable tool in the Calibrate toolbox, especially when you’re in need of a boost.  Think of this guide as a way to reboot and reset your success: an approach that will bring you a renewed sense of control over your days and reinvigorate your mission. In overhauling your eating schedule, you’ll shake up your body (and mind) to see improved metabolic markers, decreased inches, and lower numbers on the scale.