One of the questions that I am asked frequently is “do calories matter when following a low carb diet?” and the answer is “well, yes and no”. It depends on why someone is choosing to follow a low carb diet. Some people eat low carb to lower insulin resistance, others to lose weight and some want to do both. In this article, I examine lowering insulin resistance and weight loss separately.
Lowering Insulin Resistance
When we eat, the hormone insulin is released which signals our body to do two things; (1) it tells our cells to uptake energy (in the form of glucose) and (2) to store excess energy as fat.
When we are accustomed to eating a diet that is high in carbs and we eat every few hours (3 meals plus 2-3 snacks), we aren’t only eating because we are hungry and because we “choose” to eat, but because the hormones that we produce in response to the types of foods and the amounts of these food, signal us to eat.
The dietary composition of what we eat (i.e. how much fat, protein,carbs, fibre and fructose are in it) impact how much insulin is released (more in an upcoming article). When we eat foods that cause a lot of insulin to be released and we eat these types of foods every few hours, our cells become less sensitive to the signals from insulin. This is called insulin resistance.
When we are insulin resistant, our body releases more and more insulin to signal our body to deal with the same amount of glucose in our blood. Add to that stress and lack of sleep which increases cortisol levels, and these hormones and others (including dopamine and serotonin) result in our body craving specific types of food, especially carb-based food that are easy to break down to glucose. In response to the increase in some of these hormones and reinforcement by others in making us feel good when eat them, we gravitate towards sweet or savory carbs in the form of pastry, breads, pasta, chocoate …you name it.
It can’t be said enough that being overweight is not a matter of having a lack of will-power but in responding to signals from very powerful hormones that the body produces – in response to the types of foods we eat.
Unless we are quite physically active throughout the day (which most of us are not), our body does what insulin tells it to do and stores the excess energy as fat. The excess energy (in the form of glucose, the sugar in our blood) is shuttled off to the liver, where a small amount is stored as glycogen and the remainder is shipped off to our adipose cells (fat cells), to be stored as fat.
When eating a high carb diet, getting excess calories into fat cells is easy, getting the fat out of fat cells, not so much.
Eating a high percentage of calories as carbs and a low percentage of calories as fat, as well as eating foods with a high insulin index will continue to increase our insulin resistance over time.
In answer the question above, even in eating a high carb diet, insulin resistance has less to do with the total amount of calories we eat than it has to do with the dietary composition of our diet (i.e. the percentage of calories we eat as carbs/fat, the insulin index of the foods we eat) and the frequency that we eat.
People’s response to a low carb diet is different for those that are insulin resistant than for those that are not.
For those that are not insulin resistant, going without food for a significant period of time (such as from the end of supper until breakfast the next morning), causes insulin levels to drop and to transition over to burning body fat. As a result, ketones which can be used by the body as fuel instead of glucose rise.
If the person extends the time until they eat after waking up until say, lunch time, they continue to burn body fat and produce ketones – quite literally they are burning their own fat stores for energy! This wouldn’t occur if they ate every few hours, as the Dietary Recommendations encourage us to do.
These periods of time between meals where one isn’t eating or drinking foods that cause insulin release are referred to as “intermittent fasting“. It’s not “fasting” as in “starving” because we rely on, and have access to our fat stores, as fuel.
When people are insulin resistant from years of eating high carb low fat diets, as well as eating every few hours, blood glucose levels remain high for long periods after they’ve eaten. This indicates that they are not metabolizing carbohydrate well. When they go without food for an extended periods of time (such as would occur between supper and breakfast), their body is slow to switch over to burn fat and produce ketones, because their insulin levels are high.
Focusing on eating foods that cause a low insulin response, allows insulin levels to fall, which then allows one’s own body fat stores to be used for energy, as described above.
Insulin levels fall and remain low as people keep the carb content of their diet to ~ 10% of our daily caloric intake and the fat content of their diet to ~70-75% of calories. After a short period of time (~2-4 weeks) we become “fat-adapted” – which means we are efficient at burning fat for energy, rather than carbs. Ketones are produced at a fairly constant rate – which can be measured by urine dip stick, blood ketone meters or by breath analysis. Continuing to eat a low carb diet results in lowers blood glucose levels, as well as insulin levels, allowing the cells in the body to become insulin-sensitive again.
In summary, becoming insulin-sensitive has less to do with the total amount of calories we eat than it has to do with the dietary composition of our diet (i.e. the percentage of calories eaten as carbs/fat, the insulin index of the foods eaten and the amount of time between meals).
When we are eating a diet where 45-65% of the calories we eat are as carbohydrate, under the influence of insulin, excess calories not immediately needed by the cells are stored as fat.
We can’t get the fat out of the fat cells, as long as we keep taking in carbs, which are burned for energy – although people try either by restricting calories or increasing exercise, based on the old “calorie in, calorie out” model. This says that the only reason people gain weight is because they eat more calories than they burn.
Let’s look at this a bit closer…
One way people try to lose weight is by restricting calories but instead of our bodies using stored fat for energy, our metabolism slows down to spare calories, with our Total Energy Expenditure dropping by as much as 30-50%. The body does this in an effort to save calories for essential bodily functions, such as our heart beating.
In response to restricting calories, body temperature drops slightly and people complain of being unable to stay warm even with plenty of clothing because producing less heat enables the body to save calories. Heart rate and blood pressure also drop to conserve energy (calories). People find it difficult to concentrate because the brain is very metabolically active and restricting calories turns that down. Since calories are needed to move, a sudden calorie restriction leaves people feel weak during physical activity. Metabolism slows down as a survival mechanism, because the body doesn’t know when it will get another meal, and thus more glucose.
The total amount of energy we use (called Total Energy Expenditure) is not just used to move us around (exercise) but is used for generation of body heat and other metabolic processes (called Basal Energy Expenditure). This is not something which is stable, but can increase or decrease by as much as 50%. This up-regulation and down-regulation for heat and other body processes contributes more to weight loss or weight gain than exercise does.
We don’t really “choose” to eat or not eat. How much we eat (“calories in”) isn’t voluntary. As touched on above, there are hormones such as insulin and cortisol that are involved in eating behavior, as well as other hormones such as leptin, ghrelin, cholecystokinin and peptin YY that tell our body when we are hungry and when we are satiated (not hungry).
It is for these reasons that restricting calories doesn’t necessarily translate to weight loss.
Another way people try to lose weight is they increase the amount of exercise they do. They believe, based on the “calories in calories out” model, that that as long as “calories out” is greater than “calories in”, they’ll lose weight. What they neglect to consider is that “calories out” isn’t only exercise, but includes energy used to synthesize muscle, bone and other proteins.
Exercise may be under voluntary control (people can choose to exercise or not), however the energy our body uses for building tissue, staying warm, cognitive function (thinking) are completely involuntary and the body decides where energy will be used.
The problem with the “calorie in calorie out” model is that neither “calories in” nor “calories out” are under our direct control (i.e. they aren’t voluntary). Hormones that our bodies produce determine when we feel hunger and our body determines where the calories we do take in will be spent.
When we are “fat-adapted” as described above, our bodies burn fat (first from our diet and then from our fat stores), producing ketones which are used by the body, in place of glucose.
Now here is where the total amount of calories we take in matters. If there are less calories in our diet than what we need, our bodies will burn the fat in our adipose cells for fuel. This is how we get the fat out of fat cells.
When we extend the time between meals by doing various lengths of “intermittent fasting“, our bodies continue to rely on our own fat stores for energy.
So, yes, for those seeking to lose weight by means of a low carb diet, calories count.
That said, there is an advantage to eating low carb, outside of lowering insulin resistance and losing weight.
While it used to be assumed that when we eat any foods containing 100 calories (that it doesn’t matter if it is carbs, fat or protein), that 100 calories of heat is released. We now know that low carb diets provide a metabolic advantage by providing greater weight loss per calorie consumed compared to high-carbohydrate diets.
That is, on a low-carb diet, people will lose more weight per calorie than those on a high carb diet, but yes the total calories consumed still count.
In my next article, I’ll be writing about the implications regarding the foods we eat and when in a low carb weight loss diet, “Since Calories Matter“.
I tell my clients never to count calories. I don’t want them enslaved to an old way of thinking that it is all about / only about calories, because it is not.
I do all the calculations to determine how many calories they should be taking in based on their physical needs and if they are seeking weight loss, I factor that in based on a realistic estimated weight loss per week / month and determine many of those calories should be as fat, carbs and protein.
I find out from my clients what they like to eat and when, and then design their meal plan to have the desired fat to carb dietary composition that promotes becoming “fat-adapted”. For those that are insulin resistant, I help them navigate the balance between lowering insulin resistance and weight loss – by focusing on foods that trigger a low insulin response and that are nutrient dense.
I help with when to eat, what to eat and how much to eat so that all you have to do is eat!
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Ebbeling CB, Swain JF, Feldman HA, et al. Effects of Dietary Composition During Weight Loss Maintenance: A Controlled Feeding Study. JAMA : The journal of the American Medical Association. 2012;307(24):2627-2634. doi:10.1001/jama.2012.6607.
Feinman RD, Fine EJ (2003) Thermodynamics and metabolic advantage of weight loss diets. Metabolic Syndrome and Related Disorders, 1:209-219.
Holt SHA, Brand Miller JC, Petocz P. An insulin index of foods: the insulin demand generated by 1000-kJ portions of common foods. Am J Clin Nutr 66, 1264-1276
Holt, Susanne H.A.; Brand-Miller, Janette Cecile; Petocz, Peter (November 1997). “An insulin index of foods: the insulin demand generated by 1000-kJ portions of common foods” (PDF). American Journal of Clinical Nutrition. 66 (5): 1264–76. PMID 9356547. Lay summary – Insulin Index (2009-10-14).