What’s the best way to measure success with intermittent fasting?

Jumping on the weighing scales once a week might seem like the obvious choice for monitoring your weight loss progress, but this is not the only method, nor even the best: your body weight can vary by up to 2kg up or down at random on any given day without any change in the amount of fat you are carrying. This huge variation makes it very hard to work out whether the change in weight you see on the scale is ‘real’ in terms of fat loss or not. What’s more, if you are using intermittent fasting in order to improve your health, your scale weight does not tell you very much about your ‘internal’ health.

Learn why the scales don’t tell the truth

At FastDay, we have some ideas about how to measure your success more reliably.

Are you losing weight?

1) Measure your waist

If you are trying to lose weight for health reasons, the most important fat to shrink is that which sits around your internal organs (called visceral fat) and gives you a big belly. It has long been known that fat in this area increases your risk of heart disease, diabetes and other diseases, whereas fat that is carried under the skin, on your bottom, thighs, or lower abdomen, is not so dangerous. For this reason, it is recommended that your waist should measure less than half of your height. In fact studies have found that 35% of men and 14% of women have a normal body mass index (BMI) – more of this later – and yet have dangerous amounts of visceral fat.1 Intermittent fasting has been found to be one of the most effective ways of reducing visceral fat, so measuring your waist is a great way of monitoring your progress.

Learn more about the health benefits of fasting

Where is the best place to measure your waist? your natural waist which is about halfway between your navel and your ribs (between the points marked L2 and L3 on the diagram below)  is the best place to assess changes to your visceral fat.2 You should not pull the tape measure really tight, but have it resting lightly against your skin. While you might try to suck in your waist as far as you can, you can only do this once, so whether you do or you don’t, keep that the same each time you measure and you will have a good guide as to how much your visceral fat is reducing.

Where to measure your waist

2) Weigh yourself every day (or most days) and take an average

Weighing yourself once a week seems to be the standard method of monitoring weight loss in diet clubs and groups around the world, and yet this is possibly the worst way of judging how you’re progressing.  It is better to weigh yourself every day, and then take an average of several days’ measurements.

Why a weekly weigh-in does not tell the whole story:

The amount of water held in your body varies enormously: if you have eaten salty food or high carbohydrate food, your body tends to retain water and, if you weigh daily, you will quickly see the relationship between eating carbohydrates or salty foods and an increase on the scales.  Water retention can also be caused by hormonal changes in your body, and by normal muscle damage due to exercise also tends to lead to water retention. You will also find that the food retained in your system contributes to variations in your weight. So, if you have an indulgent non-fast day with salty snacks, and lots of carbs, you should not be surprised to find your weight has increased by as much as 1kg (2.2lbs) or more overnight.  This is not a ‘real weight gain and that 1kg gain is clearly not fat.

Fasting has the opposite effect, and causes a loss in water as your body uses up your glycogen reserves. Glycogen is four parts water to one part glucose, so when you burn glycogen you release a lot of water. In your early fasts you will likely burn a lot of glycogen until your body adjusts and turns to the fat stores. Thus, you may well see a big drop in weight after your first week of fasting. Only a little of this will actually be fat loss.

Learn more about metabolism

Learn more about setting a weight loss target

Your day-to-day variation in weight might be as much as 2kg, if you weigh once a week you will have no idea whether your weight on that day is at the top end of the range or the bottom. With the average rate of weight loss with intermittent fasting being around 0.5kg a week, the change in fat is completely lost in this daily variation.

If you take a look at the graph shown below which illustrates one person’s daily weights (shown as blue dots) over a 1 month period, you can see that their weight varied enormously between days. If this person did not weigh every day they might think that their diet was not working and they had plateaued or gained weight, whereas their trendline shows that they are still losing weight. Weighing daily and working out the trend line avoids this emotional rollercoaster.

Example progress tracker graph
Alternatively, weigh yourself monthly instead of weekly

If you dont want to weigh yourself most days, go for monthly instead. A month is long enough for the true fat loss from fasting to have made a difference (on average, fasters lose about 2kg/4lb per month). This means you should see the weight loss on the scales despite the possible day-to-day variations.

So, does this mean the scales are no use at all? Well, not quite, they can still be used but you need to know some tricks:

  • Don’t panic about weight fluctuations, they are completely normal.

  • Weigh every day and plot your results on a graph and see how the trend is downwards even if the day-to-day variations are large.

  • Or, weigh once a month which should be long enough for the real loss in fat to show up against the background variation.

  • Look at the overall trend. If you lose 4kg  in the first 2 weeks, and now it’s week 4 and the scale hasn’t moved, you’ve still lost an average of 2kg per week, which is higher than you might expect, so be happy!

  • Weigh yourself at the same time of day wearing the same clothing, ideally first thing in the morning after visiting the bathroom. This will help to minimize the variations.

  • Weight loss is not a steady, smooth path, but full of ups and downs, plateaus and sudden drops. When the scales don’t move, the tape measure might, so it’s best to monitor both weight and measure.

3) Body fat

When we say “I want to lose weight” we really mean “I want to lose fat”, so why not measure body fat rather than weight? Body fat analysers either as part of a weighing scale or as a separate device are widely available. They are not particularly accurate but they will show whether your body fat is decreasing. The body fat analyser works by detecting how long it takes for a tiny electrical pulse to travel through your body. The electrical impulse travels faster through water than fat and so the machine uses the speed to calculate how much fat your body has and gives you the result as a percentage of your body weight. Because it is a percentage figure, if you have a lot of water in your body your body fat percentage will be lower than if you are hydrated, so, like weighing, it is best done at the same time of day and under the same conditions each time. The  body fat analysers are particularly inaccurate if you have over 50% body fat, so bear this in mind if it applies to you.

FastDay Progress tracker

Track all your changes in weight, waist size, body fat with the FastDay Progress Trackers! Our trackers allow you to track your weight and other measures of success with a trendline so you can really see how you are doing. You can set your mini-goals and your final target and celebrate as you hit each victory. The progress tracker will also work out how many calories you would normally burn in a day and so give you an idea what your non-fast day calorie count should look like. The progress tracker will work out your body mass index for you as well.

You can also see the weight loss stats for our community as a whole and investigate how people like you have done by filtering the stats according to starting weight, gender, type of fasting. This will give you an insight into how fasting might work for you.

Find out more about the FastDay Progress Tracker

Other health improvements

1) Blood pressure. If you have high blood pressure, even a relatively small decrease in weight (as little as a 5–10% drop) should lead to an improvement in blood pressure.3 You can get your blood pressure checked at your doctor’s as well as some pharmacies. However, measuring your blood pressure when at the doctors at a random time of day can give inaccurate readings. The best time to measure blood pressure is in the morning and evening. Your blood pressure should rise as you wake up and continue to rise during the day before falling again in the evening. It is important to be relaxed and warm, sitting comfortably, not talking, not having recently exercised or eaten and with the blood pressure monitor at the same height as your heart when you take your blood pressure. This is easily done with a home blood pressure monitor. Blood pressure monitors are easily available to buy. You can choose between one that fits around your upper arm or one which fits around your wrist. Ensure you follow the instructions that come with the device on how to use it properly. Take at least three readings, a couple of minutes apart, each time you measure and ignore the first reading. Take an average of the second two and make a note of the readings. There are some good smartphone apps available for recording blood pressure readings which will show you your averages for morning and evening and even allow you to email your readings to your doctor. Ideally you should have a blood pressure of under 119/70 but anything under 139/90 is OK.

2) Blood glucose/glucose tolerance. One of the first signs of increased diabetes risk or pre-diabetes is an increase in blood glucose levels after having consumed a dose of glucose (the glucose tolerance test) or when fasting (fasting blood glucose). These tests can be done at your doctor’s or you can purchase a blood glucose monitor. Unless you have been told you are pre-diabetic, having your own monitor is probably not necessary. A normal fasting blood glucose level is between 70 and 100 mg/dL (or 3.9 and 5.6 mmol/L), whereas levels between 110 and 135 mg/dL (6.0 to 7.7mmol/L) is considered ‘impaired glucose tolerance’ and a sign of pre-diabetes.

3) Blood cholesterol tests. Most doctors consider that blood tests for cholesterol are a good indication of a person’s risk of heart disease and diabetes. Recently, however, the complexities of the many different types of cholesterol in our blood has begun to be appreciated.4 It appears that total cholesterol is not a particularly good measure of health risks. It is thought that the ratio between total cholesterol and high density lipoprotein (HDL, sometimes called ‘good cholesterol’) levels might be more relevant, but even that is not certain. A ratio of HDL:total cholesterol of under 3.5 is thought to be a suitable target. Other research suggests the ratio of triglycerides to HDL cholesterol might be a good measure. While there is so much confusion about what blood tests are best, it is hard to advise whether measuring blood cholesterol has any value for monitoring success with intermittent fasting.  Nonetheless, if you have been told that you have high cholesterol, you may wish to have them tested from time to time to see if intermittent fasting reduces your levels. Be warned, however, that during the fast itself cholesterol levels can be temporarily raised if your fast is longer than around 10 hours, so it is best to have the blood taken on a non-fast day.

4) IGF-1. One of the key potential benefits of intermittent fasting is that it may reduce the levels of insulin-like growth factor (IGF-1). IGF-1 is thought to be linked with an increased risk of cancer and it is hoped that lowering IGF-1 levels will reduce that risk.5 Lowering protein intake and restricting calorie intake have been shown to reduce IGF-1 levels. Intermittent fasting seems to have the same effect as restricting calorie intake,  but if your protein intake is high that can prevent IGF-1 levels from falling. The availability of IGF-1 testing appears to vary between different countries. It may be quite expensive in some countries. The normal range of IGF-1 varies greatly between individuals and normally decreases with age. What level of IGF-1 is acceptable from the point of view of reducing cancer risk is uncertain but cancer seems to occur more frequently in those whose IGF-1 levels are higher. Because of all these uncertainties, testing IGF-1 levels will be unlikely to be of much use in monitoring success.

Learn more about the health benefits of fasting

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