Intermittent Fasting Diets
Credit: Maena

Intermittent Fasting diets are spreading around the globe. While the concept of fasting is not new, intermittent fasting diets began picking up speed in the U.K. and made their way into the U.S. in several variations. The two most popular are The 8-Hour Diet and The Fast Diet.

The 8-Hour Diet

The 8-Hour Diet promotes the limit of food intake to an 8 hour period of your day and fasting for the other 16 hours and doing this for at least 3 days per week. The days per week you do this are not restricted. You can skip days or bundle them consecutively, it's your choice. The more you can maintain a schedule of 8 hours eating and 16 hours fasting the better your results will be.

In internet searches on this diet you will find the promised results to be quite varied. I watched several interview videos and read a few different articles and found the promised results as a range from 2.5 to 5 lbs lost per week. Giving the benefit of the doubt, I will toss this varied amount up to factors like eating healthy food, if you are doing the diet for 3 days per week or all 7, and other factors such as amount exercise.

A few things this intermittent fasting diet deems important other than the 8/16 hour feeding/fasting times are: aiming to include a list of power foods in your diet, not gorging yourself during your 8 hour feeding window and sticking to water or other no calorie drinks during your fasting time. Also, it is highly recommended to do at least 8 minutes of exercise first thing in the morning to jump start your metabolism.

The Fast Diet

The Fast Diet, aka the 5:2 Diet, promotes eating what you would normally consume 5 days per week and fasting 2 days per week. In this intermittent fasting diet, your fasting days will have your calorie intake drastically reduced. The diet calls for the average woman to eat 2000 calories on regular days (2400 calories for men) and 500 calories on fasting days (600 calories for men). For more accurate calorie numbers, you can determine your personal Basal Metabolic Rate (BMR) and your Total Daily Energy Expenditure (TDEE). Your BMR is a measure of calories burned if you did nothing but stayed in bed for 24 hours. Your TDEE is a measure of calories burned per day scaling your BMR according to your activity levels. There are a variety of calculators floating around on the internet to help you determine your numbers. Since BMR and TDEE results can vary from site to site, my recommendation is to play around with calculators on several sites and get a good average to go by. Once you determine your final numbers, you can determine how many calories to consume on your fasting days, which is 25% of your regular days. The diet promises about 1-2 lbs lost per week for women, a little more for men.

This intermittent fasting diet puts importance on not skipping breakfast. It also emphasizes lean protein and swapping carbs like pasta and breads for vegetables (except starchy vegetables like potatoes) for your fasting day dinners. It is also recommended to choose the same 2 days per week as fasting days and you must not fast 2 days in a row.

Exercise on your fasting days should be kept to a light to moderate level only if you feel up to working out. If you choose to exercise on your fasting days, make sure you stay hydrated and try to exercise when you will be able to eat within 30 minutes of completing your workout. Doing so will aid in your body's ability to recover from the workout.

Once your desired weight has been achieved, you can then move to a 6:1 format only fasting one day per week to maintain your weight.

Common Ground

At the start of these intermittent fasting diets, it is recommended to make note of your current weight, your Body Mass Index (if you have a scale or other device that measures BMI), and to take measurements of your neck and waist. For the waist measurement, I recommend measuring at the belly button instead of choosing your smallest or widest part, as these locations may be more difficult to pinpoint the exact same spot each time you measure. Retake your measurements, BMI, and weight no more than every 2 weeks.

Both diets promote healthy eating and exercise. Both diets are recommended to healthy individuals and recommend obtaining approval from your doctor before starting them. The diets are not suggested for people with: diabetes, low blood sugar or other insulin resistance issues, pregnant women, those who suffer from chronic stress, those with eating disorders, and those that have adrenal disorders.

Both claim to improve blood pressure, help to regulate blood sugar levels and cholesterol levels in addition to promises of weight loss.

My Experiment

After researching both diets, I decided I wanted to give them a try. I wanted to see if they would be difficult, and mostly, I was curious to see if they would actually work. I contacted my doctor and discussed what I was interested in doing with these diets. After he reviewed both diets and my health records, he gave me the approval to try them, although he was skeptical of how well they could work long term. He did give me caution regarding my blood pressure and told me to try to maintain a constant intake of food instead of packing all of my calories into one or two meals on my fasting days because of my blood pressure medication. He told me to monitor my blood pressure frequently on my fasting days and to ditch the diet if I saw trouble. He also prescribed me a companion medication to take with my regular blood pressure medication if my blood pressure spiked on my fasting days so I could bring it back down safely.

My goal was to attempt to run the intermittent fasting diets as accurately as I could while remaining realistic with everyday things that could get in the way. I would try each diet for a period of 4 weeks. I would not be exercising outside of calories that get burned from things beyond my control, such as walking while shopping. I did not want to plan meals out too much because many busy working people don't have the luxury of planning out every single meal of every single day. I was not be able to do the tests for blood pressure and cholesterol because I am on medications for both and they would alter the results.

Trying to determine my daily calorie limits was a bit frustrating. I played around with a number of website calculators, formulas/equations, and apps to figure out my BMR and TDEE. My overall goal for The Fast Diet (5:2) was to be between 1500-1900 on my non-fasting days. As for my fasting days on the 5:2, 25% of 1500 seemed unrealistic for me, so I aimed for the 500 calories provided as a default for the average woman. For The 8-Hour Diet I aimed for the 1200-1500 calorie range and I aimed for 7 days per week.

Opening Experiment Notes

My opinion at the moment is open but skeptical. I am not concerned so much with the chance of my body going into starvation mode because the fasting part is not severe enough or sustained for a long period of time. I'm really curious to see how the 5:2 works out since my experiences in my current routine have provided me with comparable results. In my current routine I have on occasion experienced plateaus resulting from eating well above my 1200-1300 goal for a week or two, then getting back on track. After a few days of getting back on track I would see a small weight loss each day for a few days resulting in an average of 2 lbs lost.

The 8-Hour Diet

The 8 hour feeding/16 hour fasting approach was not a difficult transition for me. Before starting the diet I determined that I was already on a fairly regular 10 hour feeding/14 hour fasting routine. The hardest part was catching myself reaching for the late night low calorie snack that I had become accustomed to. I didn't change my previous routine much in terms of calorie intake which was limited in the 1200-1300 range. I did find myself going up to 1500 calories a bit more frequently. I did not struggle with hunger during the fasting period, although I did find myself more hungry at breakfast time. Where I previously hated eating breakfast because it tended to make me nauseated, I now enjoyed it. I also stayed a bit more hydrated than with my previous routine since I was limited to water during my fasting periods.

Results & Final Review

I experienced an average of 1-1.5 lbs lost per week. The weeks when my calorie intake was higher, the weight loss was on the lower side. I was able to do this diet for 5-7 days per week. I had no adverse reactions. On a positive note, the diet seemed to make my digestion more regulated.

With The 8-Hour intermittent fasting diet, I didn't experience much difference in terms of weight loss as compared with my previous routine (reduced calorie intake program with light to moderate exercise). While it would seem tempting to stick with this diet instead of going back to my previous routine since the results were about the same without having to exercise, I know that for overall health, my routine that includes exercise, is the better way to go. I do, however, like the improved digestion that seemed to be coming from this diet. As a result, I think I will try partnering this diet with my regular routine and see how things progress.

The Fast Diet

The Fast Diet (5:2) proved to be more difficult than I had expected. I expected headaches, and I expected hunger and irritability. I was trying to aim for 500 calories and usually ended up in the 600-700 range. The hunger didn't bother me so much. I did, however, experience the following problems on my fasting days: headache/migraine, blood pressure spikes, feeling cold, fatigue, shakiness/weakness, muscle cramps in my legs and feet, and dry eyes (despite increased hydration). The days after my fasting days I was still fatigued and I ended up sleeping most of the morning away. Even after resting all morning, I would still spend the rest of the day fighting to stay awake. Planning my fast day meals in advance and spacing out my calorie intake throughout the day helped a little but it did not resolve the issues completely.

Results & Final Review

I experienced an average of 1.5-2 lbs lost per week. Definitely talk to your doctor before trying this intermittent fasting diet. I will not continue this diet. Even if, at a later time, I become a healthier individual without the blood pressure issue that caused me so much trouble, I would not try this diet again. The effects I experienced are simply not worth it to me.

Final Notes

Many people, including doctors, are skeptical if either diet can actually work and are even more skeptical as to if they can serve as long term lifestyle changes. Some that have tried these intermittent fasting diets have had success, others have not, and others are in between saying they lost no more or less than lifestyle changes that included exercise and improved diets. These diets can work, but results may vary and they may not be for everyone. Consult your doctor and decide if it's for you.

The 8-Hour Diet: Watch the Pounds Disappear Without Watching What You Eat!
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