Undertanding Bio-Elecrtical Impedance Scales
Introduction
If you’ve bought yourself a set of fancy body composition scales; but are struggling to make sense of the constantly fluctuating readings of weight, body fat, lean tissue, water content, you’ve come to the right place. In this article we lay out a guide on how they work, how to use them, and interpret the results.
At our studio we’ve been using bioelectrical impedance scales for 20 years to help hundreds of clients track changes in weight, visceral body fat, adipose body fat, muscles mass, and metabolic age. They provide great feedback on how changes in diet and exercise effect body composition, but they can be tricky to understand when you first use them. So, we decided to write an article for our clients and anybody looking to use them to monitor body composition changes. Hope you enjoy and find the article useful.
How Bioelectrical Impedance Scales work
First let’s look at how they work.
Bioelectrical impedance scales (BIA scales) use a painless electrical current to estimate your body composition, particularly body fat percentage and lean tissue. Here's the breakdown of the 4 ways that your scales calculate your body composition:
Electrical Current: When you step on the scale, a weak electrical current is sent through your body, typically traveling from one leg, up your torso, and down the other leg. We use BIA scales that also have hand sensors for even greater accuracy.
Tissue Resistance: Different body tissues conduct electricity differently. Muscle and water, which are good conductors, allow the current to pass through easily with minimal resistance. In contrast, fat tissue, with lower water content, acts as an insulator, offering greater resistance to the current.
Impedance Measurement: The scale measures the opposition to the current, called bioelectrical impedance. This impedance value reflects the amount of muscle, fat, and water in your body.
Estimation Formula: BIA scales use a built-in formula that takes the impedance value along with your age, height, gender, and activity levels to estimate your body fat percentage and other body composition metrics like muscle mass and total body water.
Readings On Bioelectrical Impedance Scales
Below are some of the measurements that might appear on your bioelectrical impedance scales:
Body Fat Percentage: This is the primary metric BIA scales estimate. It reflects the percentage of your total weight that comes from fat tissue. Its important to remember that this is not the weight of your body fat but a percentage. For example if you put on muscle but didn’t lose any body fat your body fat percentage would still go down.
Muscle Mass/ Lean Tissue: BIA scales can estimate the amount of non fat tissue (lean tissue) like skeletal muscle you have, and often displayed as a weight value in kilograms or pounds.
Body Water: This reading represents the percentage or total amount of water in your body. Generally the leaner the individual the high their water content.
Bone Mass: Some BIA scales may provide an estimate of bone mineral content.
Basal Metabolic Rate (BMR): This is an estimate of the number of calories your body burns at rest to maintain basic functions. Often scales will also provide a metobolic age alongside your BMR which indicates how healthy your metabolism is for your age, the youger being the better. I calculates according to the amount weight, body fat and lean tissue for your age, sex and height.
Weight: how much your body weighs in total.
What Factors Influence Body Composition Scales Readings
Weight
Your weight displayed on the scales is indicative of the total body weight from fat and lean tissue combined. This number alone will not tell you how much of your weight is from body fat or lean tissue. Its the simplest, most undertood data point but doesnt tell the whole story. Lets look at the factors that influence the lean tissue and fat that make up weight changes.
Lean Tissue
Changes in lean tissue readings from the scales can be due to a number of reasons, here are some.
A. Glycogen
When we eat carbohydrates (starchy and sugars), the digestive system breaks it down in glucose and the releases the glucose molecules into the blood stream. Any glucose molecules that are not used in cells will be stored in muscle in the form of glycogen to be used a handy source of energy in the the muscle for later use.
An individual with a significant healthy muscle mass can potentially store up to 500 grams of glycogen in their muscle, which will be held in place with 1500 grams of water. So muscles that are full of glycogen and water will be 2kg heavier than if they were empty.
It’s easy to see how a big bowl of pasta or a large pizza could make it appear that we’ve put on a significant amount of lean tissue; conversely if weve eaten less carbohydrates our lean tissue will appear lilghter. The good news is muscles full of glycogen means your muscles are doing a great job of extracting glucose out of the blood. But be careful, if the muscles are full of energy from glycogen and you don’t use up the energy and the next carbohdrate rich meal you eat might head towards fat stores.
B. High salt intake
The potassium/ sodium balance in the body can increase the water content of our cells thus making it appear like we have more lean tissue.
Sodium in another term for salt, and we get most of our potassium from plants and vegetables in our diet. The potassium/ sodium balance in our cells has many functions but the most relevant one here is the regulation of cell water volume: The sodium/ potassium balance helps maintain osmotic (water) balance by controlling the movement of ions and water across the cell membrane.
A diet too high in salt and too low in potassium from vegetables can cause us to retain water. Thus, if you’ve been eating a lot of takeaway foods and ultra processed foods; little veg, expect to see your lean tissue readings increase because of water retention in cells.
C. Muscle Filaments
Another reason that your lean tissue reading has gone up is you’ve put on muscle, which is always a good thing. More muscle means more strength, more metabolism, and a longer healthier life.
But muscles build at quite a slow rate, so don’t expect to see massive jumps week to week. And if you haven’t been weight training and consuming adequate protein in your diet its very unlikely the increase in lean tissue from your scales is muscle.
D. Hormonal Influences
Hormonal influences in lean tissue readings on the BIA scales are much larger in females. We recomend our females clients compare similar phases in cycles for more accurate readings. Here are some of the effects of the female hormonal cycle on lean tissue readings.
Estrogen's Role (Dominant in Follicular Phase)
Lean tissue is much more likely to go up in this phase and body fat burnt
Enhanced Glycogen Sparing: High estrogen levels, especially during the late follicular phase (leading up to ovulation), tend to promote greater fat utilization for energy during submaximal exercise. By encouraging the body to burn fat, estrogen spares muscle glycogen, leaving more of it stored for high-intensity bursts
Increased Storage Capacity: Estrogen has been shown to enhance the muscle's ability to store glycogen. This means that with adequate carbohydrate intake, women may have a greater capacity for muscle glycogen storage when estrogen is high (around the time of the late follicular and mid-luteal phases).
Enhanced Insulin Sensitivity (Follicular Phase): Insulin sensitivity is often better during the follicular phase, which facilitates the uptake of glucose into muscle cells to be stored as glycogen.
Progesterone's Role (Dominant in Luteal Phase)
Lean tissue id much more likely to go down in this phase of the hormonal cycle.
Opposing Effect: Progesterone, which peaks in the luteal phase (after ovulation), is often seen as having an antagonistic effect on estrogen's metabolic actions.
Reduced Carbohydrate Utilization: Progesterone is linked to an increased reliance on fat for fuel, which may decrease the use of stored glycogen. However, it can also limit the ability to replenish glycogen stores after intense exercise, making carbohydrate loading less effective for some women during this phase compared to the follicular phase.
Progesterone can interact with receptors in the kidneys, essentially blocking the action of aldosterone (a hormone that retains sodium and water). However, the body compensates by increasing aldosterone production, which ultimately leads to net water and sodium retention just before menstruation.
Fat Percentage Changes
A. Fat Percenetage Changes On Scales due to body fat.
Fat Loss- Fat percentages reduction on the scales can be due to fat loss. This normally occurs due to a deficit in energy below what the bodies needs. Meaning your body has expended more energy through movement and metabolism and not enough consumed from food to match its energy needs, which will lead the body to burn fat to meet the short fall.
Fat Gain- The inverse is true for fat percentage gain. Fat percentages on the scales can go up if a persons fat stores has increased due in more energy from food being consumed than is burnt through metabolism and exercise.
B. Lean Tissue Changes Effecting Fat Percentages.
Lean tissue loss increasing fat percentages. Fat percentages may also go up even when no fat has been burnt for energy. If a person loses lean tissue, less of their body is made up of lean tissue, meaning the body will now contain a higher the percentage of body fat, even if the person hasnt gained no actual body fat. How confusing!
Lean tissue gain reducing body fat percentages. Conversely, if a person gains lean tissue their body fat percentage will reduce, even if they gain no fat.
Wouldnt it be so much simpler if the scales gave body fat in weight rather than a percentage; yes it would, but unfortunately this is not the world we live in. So below is an example of how to calculate the weight of fat from your scales reading so you know where the loss in weight has come from.
How To Calculate weight of body fat.
60 kg man 22% body fat, 46.8kg.
The above example man weight in body fat can be calculated in 2 ways.
Subtract the lean tissue from the total weight= (60kg-46.8kg)13.2kg of body fat.
Calclaute the fat weight from the percentage= (60x0.22) 13.2 kg of body fat.
CONCLUSION
I’ve had to really keep it simple in this blog and fight the urge to write more as I could have wrote a book on the subject. The take away is that bio-electrical impedance scales are a great tool, they can help you understand where your weight loss is coming from i.e fat or muscle. But understanding the readings or the causes behind them can be tricky as factors like carbohydrate intake, salt, and hormones can have a big influence on readings. The scales are best used as a tool to track long term patterns as they can sometimes be misleading in the short term. At bespoke-fitness we do our best to help clients interperate the data we get from the scales and adjust diet and nutrition accordingly. Good luck