Introduction to Intermittent Fasting

Originally written for Dr. Richard Firshein, Layla Health, NYC

Intermittent Fasting (IF) has been in the spotlight for years as a popular and effective method for losing weight. It is also increasingly gaining recognition as a way to improve overall health, vitality, and longevity.

The “intermittent” aspect of IF refers to alternating periods of fasting and periods of eating. We are generally well-adapted to going without food for short periods of time because our ancestors did not always have a ready supply, and these fasting periods naturally trigger numerous health benefits.

There are several variations in the method of IF that can be used to meet different preferences, goals, or physiological needs. Some of the methods are calorie-restricted, while others are not, with normal caloric intake at restricted times.

These are the most common variations of IF:

16/8 Method: The fasting window is 16 hours, and the eating window is 8. The fast usually begins after dinner and ends with a late breakfast or lunch the following morning.

5/2 Method: Eating normally for five days and restricting calories to 500-600 on two days. The two days should be non-consecutive and spaced out throughout the week.

Alternate-Day Fasting: Alternate normal calorie days and fasting days. Fasting days can be fully without food or low 500-calorie days.

Eat, Stop, Eat: One or two fasting days per week. The fasting window is 24 hours and is usually from the end of dinner to the beginning of dinner the following day.

The Warrior Diet: Most of the day is spent in a fasting state, with a 4-hour window for one substantial meal in the evening. Some amount of light snacks, usually fruits and vegetables are allowed during fasting times.

Health Benefits of Intermittent Fasting

There is a growing body of research that suggests IF can be an effective way to lose weight, improve overall health, and resist chronic illness. These beneficial changes happen when our bodies run out of glucose as an energy source and begin using fat stores.

After a meal, our body breaks down carbohydrates into glucose for fuel. When it runs out of free glucose, it turns to glucose stored in the form of glycogen in the liver. When glycogen stores are depleted, it turns to fat stores. This releases fatty acids that are converted to ketone bodies, which are another source of fuel for cells.

The transition from using glucose to fat is gradual and begins about 10-16 hours after the last meal. At this point, the body begins entering light ketosis (using ketones as fuel) and continues to a full state of ketosis if the fasting period is long enough. The health benefits of using ketones instead of glucose are the reason why many people follow the keto diet. IF mimics many of those benefits.

The fasting state is natural for us even though most people do not fast regularly. Our modern times have allowed us to enjoy three meals per day, but our ancestors hardly ate this way. For most of human history, people had to endure periods of fasting due to lack of food. Not only are our bodies adapted to periods of not eating, there is more and more evidence showing that it is the more optimal state.

Given modern research and developments in health and fitness, we now have the option of harnessing these healing changes once we learn how to do so effectively. Some of the most studied benefits of IF are:

Promotes weight loss: In addition to the obvious benefits of restricted caloric intact, IF has been shown to optimize weight loss by increasing metabolism. Also, because the body switches to fat-burning during fasting periods, IF has been shown to better target areas of problematic fat accumulation, such as abdominal fat and fatty liver.

Increases insulin sensitivity: Increases insulin sensitivity in those with insulin resistance and improves blood glucose balance.

Improves cardiovascular health: Studies show that IF lowers systolic blood pressure, heart rate, and blood levels of triglycerides and LDL cholesterol.

Decreases inflammation: IF decreases inflammatory markers.

Improves brain health: Improves cognitive performance and memory.

LONGEVITY BENEFITS:

Promotes cellular renewal: Triggers the process of autophagy, which recycles old or damaged cells in the body, getting rid of built-up waste and cellular debris, improving the metabolic functions of cells, and reducing oxidative stress.

Triggers adaptive cellular stress response: Enhances cellular ability to resist injury and disease.

Naturally increases Human Growth Hormone: (HGH). HGH has many important functions in the body and plays a role in longevity. However, the production of this hormone subsides as we age, and IF is a natural way to boost it.

Is Fasting for Everyone?

In short, no. While many people can enjoy the benefits of IF, there are some cases where fasting can induce unfavorable changes. Fasting may not be right for you if you experience the following:

• Underlying hormonal imbalances or thyroid issues

• Significant stress or insomnia

• Low blood sugar or diabetes (diabetes patients may be able to practice IF under the supervision of their physician)

• Eating disorder

• Gallstones or gallbladder issues

• Women who are trying to conceive

It is best to consult a healthcare professional before starting IF to determine if it is a good fit for you and find the most suitable approach.

Is Intermittent Fasting a Diet?

When people think of “going on a diet” it usually means making short-term changes to achieve a goal, such as weight loss. IF can be used this way, but its value is harnessed to the fullest capacity when it is practiced long term as a lifestyle. More and more research supports that over the long-term, IF can nourish and optimize your health, promote longevity and decrease chronic illnesses.

If we consider the term “diet” in the broader sense of food choices, whether it’s Mediterranean, paleo, plant-based, vegetarian, keto, or one of the modern variations, IF can be used in conjunction with and to enhance the benefits of any of these.

Considerations for Women

Intermittent fasting (IF) can be extremely beneficial for many people, but differences in our physiology can lead to different responses to the fasting state. Women tend to be more sensitive to hormonal fluctuations than men and are therefore more vulnerable to developing hormonal imbalances while fasting. However, most women can still enjoy the benefits of IF if they learn how to do so safely.

Since women’s bodies are more sensitive to hormones, they are more likely to be affected by the hunger hormones leptin and ghrelin as their levels increase during a fast. This can lead to overeating after the fast, and the cycle of undereating and then overeating can cause a hormonal imbalance.

On the other hand, eating too few calories can lead to an imbalance for women as well. Insufficient calories can negatively affect women’s reproductive hormones, disrupting the menstrual cycle, or even stopping ovulation.

A higher hormonal sensitivity may also negatively affect blood sugar levels. One study found that alternate-day fasting impaired women’s blood sugar levels but did not have this effect on men.

It may be difficult to tell if the sensation of hunger is within what is considered normal and safe, or excessive, especially in the morning, when a surge in transient hunger is common. It is important to pay attention and understand your hunger threshold because ignoring it excessively can lead to overeating or not eating enough.

Of course this does not mean that women cannot or should not practice IF, but simply that they should do so more cautiously, being aware of hunger or any other symptoms that may arise.

Crescendo intermittent fasting

Crescendo fasting is a milder form of IF that can be practiced by women who are sensitive to fasting, or by anyone who is beginning a fasting practice. In this variation, the time-restricted 16/8 method is adjusted.

Instead of fasting every day, fasting days are limited to 2 or 3 days per week. These days should not be consecutive, with at least 1 non-fasting day after each fasting day. The fasting window can be shortened to 12-16 hours as well, depending on how you feel when you are fasting.

As you get used to periods of time without food and feel good on this schedule, the fasting window can be gradually lengthened to the full 16 hours, or more fasting days added.

Tips for Successful Intermittent Fasting

Eat nutritious foods: It may be tempting to overeat or eat less nutritious foods after a fast, especially if you are feeling hungry or feel that you have cut back enough calories to indulge a little. However, it is important to remember that the goal of fasting is improving overall health. Eating healthy nutrient-dense foods will help you achieve your health goals faster and more effectively.

Drink extra water: Proper hydration is essential during fasting times as well. A portion of our daily water intake comes from fruits and vegetables, so when we restrict eating times, we may inadvertently restrict our water intake. More water is also flushed out during a fast, so it is extremely important to be aware of any dehydration signs, such as thirst, headaches, and dry mouth, and remember to drink extra water.

Adjust exercise: While exercise is beneficial, you may want to minimize the intensity during fasting times or days. Higher intensity exercise can be performed on non-fasting days.

Know your supplements: It is generally safe to take supplements while fasting, but you need to ensure that you are taking them at the right times to maximize their benefits. Some supplements need to be taken with food to be absorbed; taking them during the fasting window can make them less effective. Other supplements can raise your insulin levels (taking you out of a fasting state) or can lower your blood sugar. Make sure that you know what your supplements do and when to take them.

Working with a Health Coach: If you would like to try IF but are new to fasting or have had a difficult time fasting in the past you may consider working with a health coach. A health coach can explain the differences in the fasting methodologies and help you find the approach that works best for your lifestyle and physiological needs.

Fasting generally takes mental and emotional effort. It is not easy to change our routines – even if the changes may be worth it! Periodically checking in with a coach helps establish accountability and provide mental support while keeping you on track, until you have established IF as a long-term eating pattern and have enjoyed the benefits of this method.

Summary of Intermittent Fasting

• IF alternates fasting and eating periods, and triggers burning fat for fuel in the fasting state. Fasting periods range between 12 and 24 hours.

• Studies on IF are showing significant health benefits, including weight loss, increased insulin sensitivity, cardiovascular and brain health, and reduction in inflammation.

• It is important to know if you have any conditions that can make fasting not right for you.

• IF works best as a lifestyle choice and can complement other diet plans.