The research is promising: Intermittent fasting may positively affect longevity, brain, and metabolic health. According to several studies, this type of fasting can show improvements in insulin sensitivity, cholesterol, and triglyceride levels as well as aid weight loss and mitochondrial efficiency. Intermittent fasting can also influence and affect your blood glucose levels.
But intermittent fasting isn't always as simple as fast-eat-repeat. Of course, that's not to say it's complicated. But when you're about to break your fast, it can help to keep in mind how different hormones work together during times of fasting and eating.
Here's an interesting finding from a review regarding the impact of macronutrients on the hunger hormone ghrelin (produced in the gastrointestinal tract). It found that while carbohydrate intake quickly suppresses ghrelin due to its quick absorption, protein has the best capacity for the long-term suppression of ghrelin. Ghrelin increases twofold before food ingestion and then falls rapidly within an hour of eating.
Interestingly, individuals with obesity do not show this decrease in ghrelin levels compared to people in average weight categories. So, this can lead to continued hunger and continued eating. This suggests that breaking a fast with protein can help avoid any significant responses in glucose that could increase glycemic variability and insulin levels throughout the day. So, how do we put this into action?
What Can You Eat During a Fast?
First of all, it's helpful (and essential) to know precisely what you can and cannot consume during your fasting period. This will help keep you from accidentally breaking your fast before you mean to. For example, black coffee, tea (green or herbal), and broth are all allowed when you’re fasting for metabolic purposes. For stricter fasts, like in the case of those who may be fasting for gut health, it’s often a good idea to stick to just water.
However, there's some debate over whether or not non-caloric sweeteners like stevia, sucralose, and aspartame break the fast. Still, because they can cause your body to release some feeding hormones in anticipation of calories, avoiding them is the typical recommendation. Staying hydrated during a fast will be critical, especially for a more extended fasting period. Making your own electrolyte drink with water, lemon juice, and a pinch of salt can help for longer fasts—electrolytes begin to be flushed out as ketones increase.
If you're doing more of a "fat fast," you may consume full-fat dairy, coconut oil, and MCT oil. This is not technically a true fast, but it may help increase fasting time and boost ketone production.
What to Eat When Breaking a Short Fast
While there is less to consider when you're breaking a fast that you've been on for less than 24 hours, you should still pay attention to your first meal of the day to reap the maximum benefits of fasting. You will be much more sensitive to carbohydrates after fasting, so consuming larger amounts of these foods may increase your risk for a glucose spike.
How to Break Your Fast
A good rule of thumb is to focus on protein first after fasting to promote a smaller glycemic response. From there, you can enjoy some low glycemic carbohydrates and healthy fats in your main meal, ideally around 30-60 minutes later. For example, some lean protein like turkey or a whey protein shake are good options.
Foods like bread, bagels, and cereal, will typically cause glucose to spike quickly after fasting and may cause an "energy crash," promoting more feelings of hunger and lethargy throughout the day. Though you should try to eat most carbohydrates during daylight hours to align with your circadian rhythms, the kind of carbohydrates you eat and what you pair them with matters. Choosing complex, fiber-rich carbohydrates that are low in the glycemic index is a good choice here. Think avocado, berries, flaxseed, chia seeds, steel-cut oats, and squash.
Portion Size Matters
And what about portion size? That matters too. If you eat a large meal because you're really hungry coming off your fast, try to have a small portion first, see how you feel satiety-wise, and then go for seconds if you're still hungry. Eating too much too quickly can cause digestive distress or bloating, so eating slowly and mindfully here is a good idea.
Some sample meals for breaking a short fast:
- A piece of cheese 15 minutes before eating steel-cut oats with protein powder, nuts, and berries.
- One hard-boiled egg 15 minutes before eating a meal such as salmon, steamed vegetables, avocado, and feta.
- One or two pieces of sliced turkey 15 minutes before eating unsweetened Greek yogurt with berries, nuts, chia seeds.
What to Eat When Breaking an Extended Fast
An extended fast is when you've been fasting for 24 hours or more, and coming off it can be tricky. Just for a bit of background on what's happening in your body coming off of a fast: after 24 hours of fasting, most people's glycogen (stored glucose) stores have been significantly depleted. Your body then begins to burn stored fat for energy. Your body breaks down fat through lipolysis, causing free fatty acids to enter your bloodstream and be utilized for fuel through beta-oxidation and ketone body formation. Between 24-72 hours of fasting, ketone bodies become your body's primary energy source. Additionally, the body creates new glucose from glycerol and amino acids through gluconeogenesis to supply the brain and red blood cells with glucose.
Your Hunger Hormones
So, what happens to hunger? One study showed that although ghrelin rises and falls in a cyclic pattern related to your circadian rhythm, total ghrelin levels decrease every 24 hours of fasting. So, by day three, overall ghrelin output was lower than days one and two. These results may explain why overall hunger levels seem to decrease around the third day of a fast. Ghrelin triggers your stomach's parietal cells to start secreting the digestive juices and stomach acid we need to break down incoming food.
What to Eat After Fasting
When breaking an extended fast, try to focus on small portions and easily digested foods. Since your body has been without food for so long, it may not be used to producing the digestive enzymes you need to properly break your food down.
Try some bone broth soup and well-cooked vegetables as the first meal after a long fast. Another idea is to sip on some broth for an hour, then eat a small first meal. You could also include some apple cider vinegar with lemon water as part of your first meal. This can help increase digestive capacity as you ease back into eating.
How Much Should You Eat?
It’s important to stick to small portion sizes at first to optimize your glycemic response. Try to stop eating when you feel about 75 percent full. Overeating within your eating window will likely blunt the positive effects of fasting, causing insulin and glucose levels to spike quickly. Grazing through your eating window will stimulate the insulin-mTOR sensing pathway, which leads to lipogenesis (or fat creation and storage).
Timing When Breaking a Fast
Does the time of day you break your fast matter? In short, it could! Nutrient-sensing pathways are closely connected to circadian clocks and fed/fasted states.
The timing of the fed and fasted state also impacts your metabolic health, which further confirms the importance of meal timing and eating within a time restricted window. One study found that dawn to sunset fasting had positive ramifications on obesity, NAFLD and metabolic syndrome. Another determined that eating within a ten hour window helps improve cardiometabolic health in those with metabolic syndrome.
Nighttime eating negatively impacts specific glucose and fat regulation/metabolism genes. Many human studies on shift work and jet lag have similar findings. Eating and sleeping outside of circadian rhythmicity increase the risk of disease, specifically obesity, diabetes, and cardiovascular disease. Breaking a more extended fast during daylight hours (if possible) can help combat this effect!
Differences in Gender
For women, there is another consideration as well. During a longer fast, your thyroid levels may drop, so you want to make sure you help restore your thyroid hormones to normal levels when you're coming off a longer fast.
Eating thyroid-supportive foods containing zinc, iodine, and selenium is helpful here! Include things like walnuts/almonds, seafood, seaweed/iodized salt, and brazil nuts in your main meal to help support your thyroid. It's also crucial for women to include a mixed macronutrient meal containing some carbohydrates, protein, and fat in their fast breaker. Women can respond to fasting much differently than men, so when in doubt, consult your care provider to see if fasting is right for you.
What Not to Do When Breaking a Fast
You now know what to do when breaking a fast, but what should you avoid doing? It may seem pretty obvious, but try to avoid large portions or heavy meals right off the bat. It's also a good idea to steer clear of refined/starchy carbohydrates all on their own. Basically, pizza shouldn't be your first choice! These foods tend to be calorically dense but nutrient-poor. Additionally, raw foods like salads, unroasted nuts, or vegetables can be hard to digest, so avoiding these in large amounts may be helpful.
Try to avoid being sedentary right after breaking your fast. Another reason to avoid a large meal right away is that it will make you sleepy. Taking a short walk after eating is also a great way to help handle any incoming glucose from your fast breaker. Let's look at a new systematic review published in the Sports Medicine journal to explain this. The review looked at 51 different studies and found that just 30 minutes of acute post-meal aerobic exercise (like walking) effectively lowered both glucose and insulin levels versus not being active after meals at all.
As a final reminder, try not to overeat within your eating window! If you consume several thousand calories more than you need from processed foods, you won't be reaping the same weight loss, longevity, and metabolic benefits that you'd experience from a more controlled caloric intake. Eating without distraction, making your meal last for 20 minutes or more, and practicing mindfulness while eating can create a positive connection with your first meal after breaking a fast.
A Typical Glucose Response
Want to see what breaking a fast looks like for your glucose levels? In the image below, you can see a typical glucose response when breaking a short fast with carbs versus with a protein-focused meal. On the left, you can see the spike highlighted in green that represents what happens to your glucose after a protein-filled breakfast to break the fasting period. On the right, the highlighted spike indicates your glucose response after breaking your fast with carbs.
Both these responses are ‘good’ responses, but the protein-focused meal produced a much smaller shift in glucose, which can be tied to lower glycemic variability and more stable energy levels.
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