What's the deal with intermittent fasting and why is this dietary approach getting so much attention? We've broken down what the science says about the potential benefits intermittent fasting may have for your health.
What is Intermittent Fasting?
Intermittent fasting is a dietary approach that focuses on time-restricted eating, fluctuating between periods of fasting usually lasting longer than 12 hours.
You may already be intermittent fasting to some extent and not even realize it as intermittent fasting is thought to help us follow our body's natural circadian rhythm.
If you tend to eat an early dinner, skip the late night snacking and don't eat till breakfast the next day, then you've experienced intermitittent fasting!
There are many styles of intermittent fasting, which makes this a more approachable practice than most would think. Two of the most popular intermittent fasting approaches are:
- The 16:8: involves extending your nightly fast, taking 12-16 hours between dinner and breakfast the next day. For example, you may eat dinner around 6 pm and then nothing else until 6-10 am the next morning.
- The 24 hour fast involves fasting for 24 hours 1-2 times a week; you'll still consume non-caloric beverages like water and unsweetened tea.
It might seem a little crazy to imagine not eating for longer than 8 hours, but in all reality our body needs time to rest, relax, and process nutrients; tending to our normal repair functions to maintain our health. Additionally, we already have a natural fasting rhythm that occurs when we sleep.
When thinking about adding a fasting day into your lifestyle consider that you want to find a style of eating, not dieting, that works for you. Be sure to look at your work schedule, sleep schedule, and lifestyle when deciding what type of fasting schedule may work the best.
How Does Fasting Work?
Our bodies put in a lot of work when it comes to processing the food we eat to provide us a consistent source of energy.
When we eat food is broken down into macro and micronutrients via digestive enzymes. Carbohydrates like rice and starchy vegetables get broken down into glucose to be absorbed into our bloodstream and utilized for immediate energy with the help of insulin.
When our cells don't use all of the glucose from the food we eat it gets stored in our liver and muscles as glycogen. And when in a calorie surplus, any leftover fuel gets store in our fat cells, as fat.
In-between meals, and when we first start fasting as long as we aren't snacking, our body will utilize glycogen and some stored fat for energy. But once our glycogen stores are depleted (typically between 12-36 hours after our last meal) our body will begin to break down more fat for fuel (1).
Prolonged fasting will eventually prompt our body to experience ketosis and metabolically switch to breaking down fat as fuel; using stored fatty acids instead of glycogen for energy (1).
Benefits of Intermittent Fasting
Some studies suggest that adopting an intermittent fasting practice may help with weight loss, improve memory and mental performance, cardiovascular health, type 2 diabetes, and the effectiveness of cancer treatments (2,3).
While much of this research comes from animal studies, emerging human data has offered promising results - especially related to the potential for helping with weight loss and improving some aspects of nutrition-related chronic diseases such as diabetes and heart disease (2,3).
It's important to note that the long-term effects of intermittent fasting have not been fully established, but current research shows some promising short-term benefits that we've outlined in our list below. Additionally, while the potential benefits of fasting are exciting, there is not enough research to proclaim it is more effective for weight loss or improving health than a basic healthy eating approach.
1. Supports Weight Loss
It is well understood that how much you eat is a much stronger determining factor for weight loss than how often or when you eat (4). However, intermittent fasting may help you sustain a caloric deficit leading to weight loss.
But just because you are intermittent fasting does not necessarily mean you are in a caloric deficit. Some people still struggle to stay within a healthy caloric range even when they restrict the time frame in which they consume their meals.
Use this caloric calculator to help you determine what a healthy caloric range is for you diet and lifestyle.
Caloric restriction has been proven as a way to reduce body weight and visceral fat but it can be difficult to sustain a healthy caloric deficit for long periods of time (2). Intermittent fasting is thought to be a good tool to support weight loss as emerging human trials show meaningful reductions in body weight and visceral fat (2,4).
Intermittent fasting is a hard intervention to study long-term because it can be difficult to get people to eat less and fast at the same time, and factors like protein intake, time spent fasting, and quality of the diet can impact potential findings. Further studies are needed to determine any long-term weight loss benefits of intermittent fasting, as it is unclear if yo-yo dieting or weight gain is likely to occur when fasting is stopped.
Weight loss from intermittent fasting may also be about more than just energy restriction. Alterations physiologically from fastings, such as reductions of insulin and the hormone leptin, may lead to more weight loss than what we would achieve by just cutting calories alone (5).
At the end of the day, sustainable weight loss is more than just managing our caloric intake through practices like intermittent fasting. Our lifestyle, stress levels, sleep regime, and other factors all affect our ability to lose and maintain a healthy weight.
2. Improves Insulin Resistance, Which Can Help Diabetes Prevention and Management
Intermittent fasting and weight loss may help reduce fasting blood glucose and improve insulin sensitivity through lowering concentrations of leptin, the hormone produce by fat cells to regulate hunger, and increasing adiponectin, a hormone that plays a role in glucose and lipid metabolism.
In some studies where fasting was used as a weight-loss intervention and strategy for maintaining a healthy weight, people who intermittently fast had lower levels of blood glucose which happens to be a central goal in the prevention and treatment of diabetes (4,6).
These possible benefits may be driven more by reductions in body weight and body fat percent stemming from caloric restriction influenced by intermittent fasting, but research still shows an overall positive effect on blood sugar levels when intermittent fasting (4).
Intermittent fasting may help improve glycemic control and insulin resistance with a reduction in weight in those with diabetes and those without.
3. Could Help Lower Cholesterol
Your cholesterol might also improve after intermittent fasting when consuming a healthy diet during your non-fasting periods.
Better lipid profiles have been found after intermittent fasting including lower overall cholesterol, lower LDL (low-density lipoprotein), and lower triglyceride levels in healthy and overweight populations (7,8).
The majority of studies investigating intermittent fasting's effects on cholesterol have focused on those fasting for Ramadan, so intermittent fasting may be an effective dietary method to improve your cholesterol, but further studies are needed to explore the differences in short-term vs long-term metabolic changes associated with fasting. (8).
If you're concerned about high cholesterol try adopting healthy lifestyle habits like incorporating exercise and a diet low in saturated and trans fats, and rich in high fiber foods.
4. Promotes Heart Health
- reducing blood pressure
- lowering blood lipid and cholesterol levels
- stabilizing blood glucose levels
- decreasing inflammatory factors such as C-reactive proteins and cytokines
The reduction in calories along with metabolic shifts from intermittent fasting may also help reduce your resting heart rate (HR). elevate your heart rate variably, and improve vasodilation and blood flow (10).
While this may seem exciting, people don’t always respond the same as animals to these interventions and more studies need to be done in people to understand the role of intermittent fasting in heart disease. Additionally, the quality of your diet is crucial for heart health benefits.
A heart-healthy diet high in nutrient-dense whole foods from whole grains, fruits, vegetables, and quality proteins is still the best approach to supporting heart health.
5. May Help Manage Inflammation
Our bodies naturally undergo inflammation as a part of the process it uses to fight off harmful pathogens or recover from injuries by triggering our immune system.
However, when inflammation persists for too long it can start causing us harm. Chronic inflammation happens when the immune system continues to be triggered by what it thinks is a threat. Prolonged inflammation plays a role in the development of chronic health conditions such as atherosclerosis, heart disease, osteoporosis, and even diabetes (11).
Intermittent fasting has been shown to reduce concentrations of pro-inflammatory markers such as homocysteine, interleukin 6, and C-reactive protein which play a role in the development of these chronic diseases (3).
Although fasting may provide some health benefits, looking at the quality of our diet and lifestyle can help us create healthy habits to support our health.
6. Supports Brain Health and Function
Keep in mind that it's not simply the act of fasting alone that may have these potential benefits, decreased inflammation, reductions in body fat, and healthier blood sugar levels have all been linked to healthy brain function.
7. Keeps Cells Healthy and Vibrant
When we fast we give our body time to rest and repair, tending to natural processes put in place to keep our cells healthy. Autophagy is an example of a process our body naturally undergoes to keep our cells healthy and in turn, keep us healthy!
Autophagy is the process our cells go through to remove waste and dysfunctional cells to help our body clean out damaged cells and regenerate new and healthier cells. Evidence suggests when we intermittent fast, we increase the frequency of this process, so our body works harder to remove any unwanted junk and dysfunctioning cells (13).
Increased autophagy may play a role in protecting us from several diseases including neurodegenerative diseases, cancer, inflammatory diseases, and cardiovascular diseases (13).
8. May Increase Your Life Span
There are several reasons that intermittent fasting may positively impact our life span; weight loss, decreased blood pressure, and most of the benefits we listed above may all contribute to prolonging our life while increasing our quality of life at the same time.
Intermittent fasting has been found to affect longevity in animal studies, having beneficial effects on life span and markets for health, stress, metabolic response, and age-related diseases (13).
These findings are hard to confirm in human trials as there are many factors that affect epidemiological studies and many different types of fasting. But at the end of the day, some of the benefits of intermittent fasting may increase our quality of life overall and reduce our risk of developing chronic diseases.
9. May Play a Role in Cancer Treatment and Prevention
This potential benefit is still a bit up in the air. Animal models have shown that periodic fasting may help protect normal cells from the toxic effects of chemotherapy drugs while sensitizing cancer cells to the treatment (2).
When it comes to human trials, the data is still inconclusive. Weight control and reduced inflammation in the body could reduce the development of cancer, but further research is needed to understand the role fasting may play in cancer treatment (2).
10. Could Help Promote Balance in Other Areas Beyond Food
When we think of intermittent fasting we immediately think of food, since that is what we are limiting. But could we benefit from taking a break from other things in our life?
The basic concept of fasting is to abstain from something for a specific period of time, so what other things could we fast besides food?
Television, social media, and video games to name a few may all be things we could use a break from that may positively impact our health and well-being.
At the end of the day, consciously choosing to reduce or shift our habits can help us create health and wellness goals based on our values and beliefs.
Are There any Cons to Intermittent Fasting?
So far, the effects of intermittent fasting seem overall positive. But there can always be a downside to every diet if it’s not approached in the right way.
Here are four potential risk factors or "cons" associated with intermittent fasting:
1. Intermittent Fasting Can Still Lead to Weight Gain
Feeling starved during your fasting period might make some people more prone to binging behaviors when they’re not fasting. And eating more calories than what your body burns will lead to a long-term increase in body fat even if you consistently fast for 12-16 hours each day.
In other words, if you are having trouble maintaining your hunger and end up going completely rogue on your non-fasting periods, you could end up gaining weight.
Going rouge during your non-fasting periods can sabotage your health goals, start a meal prep routine or plan your meals to ensure you're nourishing your body.
Not sure what style of diet is right for you? Use a meal plan quiz to get started!
Intermittent fasting doesn’t replace healthy eating or calorie control; you can still gain weight when fasting if you're eating more calories that what your body burns.
2. Skipping Meals Can Cause Headaches, Dizziness, and Nausea
Long periods of fasting can lower your blood sugar levels and leave you feeling lightheaded, dizzy, with headaches, and/or nausea.
If you have a medical condition, talk to your doctor to make sure it's safe to try intermittent fasting. People with type 1 diabetes and/or on diabetic medications may be more susceptible to unwanted side effects or struggle with controlling their blood sugar levels (14).
Your body will also need some time to adjust, so try choosing a day of the week or period of time that you don’t need to be very active or deeply concentrate when first starting a fasting practice.
3. Restrictive Eating Can Influence Disordered Eating
Any diet that supports skipping meals or restrictive eating can trigger some not-so-great food relationships. Especially when the positive weight loss effects are directly impacted by not eating, or restricting food intake.
This isn't a great mindset to go into fasting with and can lead some people to take intermittent fasting too far, developing disordered eating patterns, or getting caught up in a yo-yo dieting cycle.
Not to mention that not eating enough calories each day to meet your basic needs can lead to nutrient deficiencies, decrease your immunity and create havoc in your body.
Whatever your reason for wanting to intermittent fast, remember to incorporate basic nutrition principles including calorie control and a balanced diet to set yourself up for success.
Going rouge during your non-fasting periods can sabotage any hopes you have for reaping the health benefits when intermittent fasting.
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