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Weight Loss: It Really Comes Down to Calories

It comes as no surprise that people are understanding more and more that nutrition does in fact play a large role (primary role, perhaps?) in weight loss. For the most part, there are weight loss diets that can create success for those who take the initiative to learn about food in the dieting process, however for those weight loss diets centered on purchasing specific products (whether it is pre-made foods/drinks, supplements, etc) there seems to be a gap in gaining nutrition-related education causing those dieters to fail to make meaningful life-long changes in their eating habits. For the most part, a successful weight loss diet will involve actively learning about food and making food choices (i.e. NOT mindlessly eating whatever is provided in the pre-made supplementary foods) and tracking intake of food (food journaling, tracking calories/macronutrients). Why? Having an understanding of foods, their caloric/macronutrient content, and how these foods compare to your specific needs sets the base for a lifetime of making appropriate food choices, no matter the circumstances.

To put it simply: yes calories count, and not all calories are created equal. My last few posts went into detail about the three macronutrients: protein, carbohydrates and dietary fat. It should be noted at this point that calories coming in from the three different macronutrients will ultimately have different fates in the body, and thus eating enough (and appropriate amounts) of each of the macronutrients for your needs is the key to achieving nutritional balance. *See the previous posts on protein, carbohydrates and dietary fat as a reference.

So what exactly is a calorie?

A calorie is a unit of energy. Technically a calorie (kilocalorie in nutrition, but we will call it a calorie here) is the amount of heat required to raise 1kg of water by 1 degree Celsius. (Nix, 2013) All you need to know is this: a calorie is a unit of energy, as in energy in the form of food coming in and energy that is expended. (Nix, 2013) That's it. A calorie is not inherently good or bad, but rather a unit of energy to where you require a certain amount in order to fuel your body to maintain normal processes. Being in caloric balance indicates that you are eating enough calories to foster your needs based on your body composition and activity level. With increased energy expenditure (like increased physical activity, periods of growth, rebuild/repair of injury, illness, etc) you will need additional calories to balance this increase in energy expenditure. Calories (or energy) in excess of what you need will become stored energy (body fat, liver and muscle glycogen) but where a deficit of calorie intake (taking in less than you are expending) can lead to utilization of these stored energy forms in order to provide that necessary energy. (Energy has to come from somewhere; it cannot be created nor destroyed but rather transferred. In the case of a caloric deficit, stored energy would be utilized to make up for the imbalance of intake to output.)

Without going in to too much detail, it is important to understand that calories (energy) in food come in the form of the macronutrients (carbohydrates, protein, dietary fat). Non-caloric components of food include water, fiber, and micronutrients like vitamins, minerals, and phytochemicals. For this post, we are focusing on the macronutrients as we discuss energy balance, but do not assume that non-caloric food components are unimportant. On the contrary, they play an equally (if not more) important role than the macronutrients, but we will dive into this discussion on a future post.

So we take in calories in the form of macronutrients, but we USE calories in multiple ways. There are three major components to your daily energy expenditure (calories burned everyday) which includes your resting energy expenditure, thermic effect of food and physical activity. (Hall and Guo, 2017) Your resting energy expenditure (REE) is the amount of energy used in simply maintaining bodily functioning (when not being physically active) and is the largest contributor to your overall caloric expenditure. (Hall and Guo, 2017) This means that the majority of calories that you burn everyday are being used to just maintain functioning when you are not being physically active. There are variable differences in this REE based on body composition where metabolically active tissues require more energy; and what may seem surprising to some is the fact that obese individuals actually have MORE metabolically active tissues than lean individuals, and thus expend more calories than a lean individual through just their REE alone. (Hall and Guo, 2017)

**As a side note: adipose tissue (body fat) IS a metabolically active tissue (contrary to the belief that body fat is simply 'dead weight') where for example it proportionally secretes the hormone leptin. (Hadley and Levine, 2009) This means that the more body fat there is, the more leptin is secreted. Leptin is specifically associated with signaling satiety (tells the brain that you are full; stop eating). (Hadley and Levine, 2009) This occurs as a way for the body to feedback to the brain that it does not require more energy intake due to its current storage capacity. (Translation: having higher amounts of body fat signals the brain to NOT continue eating) When adipose tissue is lost OR energy intake is low, this leptin signaling also decreases which means that the brain is no longer getting this signaling to stop eating, i.e. allowing for increased energy intake; continue eating (again as feedback from the body that stored energy is getting low or that energy intake is not sufficient, so continue eating). It is likely due to this leptin signaling that individuals who currently have high amounts of body fat may not eat much throughout the day or even feel hungry at all. (This is often the first obstacle to overcome for someone who is currently overweight/obese to try to eat more calories to meet their needs as they simply do not feel hungry.) Once the leptin signaling starts decreasing (in response to decreases in body fat), then it becomes easier to eat more calories throughout the day and there are noticeable feelings of hunger. Add to this the fact that leptin signaling decreases when energy intake is too low, and now there is a probable cause for those insatiable appetites and inevitable binges that come from crash dieting or very low calorie diets.

Back to how we USE calories...

The thermic effect of food is the energy required to digest, absorb, store and metabolize food and as such remains steady at about 10% of caloric expenditure for everyone. (Hall and Guo, 2017) The REE and thermic effect of food are difficult to change or control, but where energy expenditure through physical activity is the most variable between individuals as it can be controlled. Physical activity energy expenditure includes purposeful exercise and non-purposeful exercise or activities of daily living (cooking, cleaning, self-maintenance, etc). (Hall and Guo, 2017) To this point, when we discuss energy expenditure, we are including all of the above components whereby your body is burning through a given amount of calories every day, and therefore you require an equal amount of calories through food everyday to maintain that functioning. When it comes to efforts to lose weight, then the use of a caloric deficit (taking in less calories than are being expended) is therefore theorized to utilize stored energy forms (as body fat AND lean body mass) in efforts to provide calories for daily energy expenditure. (Hall and Guo, 2017)

Now about this caloric deficit...

If seeking weight loss, then a caloric deficit is the goal. A caloric deficit essentially means that there is a negative balance to what is being taken in (energy in the form of food being eaten) compared to energy being expended (energy being used for physical activity and normal bodily functioning). The previous theory regarding a caloric deficit was based on the assumption that 1lb of fat is equal to 3,500 calories, and thus if in a 500 calorie deficit everyday for one week (seven days) you should theoretically have accumulated a 3,500 calorie deficit, or 1lb of fat lost. (Hall 2007) This theory however has been largely abandoned as it does not take into account the loss of lean body mass during weight loss or the variability in individual energy expenditure, energy requirements, and hormonal state of the individual. (Hall 2007) Add to this the fact that most of the weight that is lost when beginning a new dietary regimen includes water, digestive bulk and glycogen loss followed by a combination of fat mass and lean body mass. (Hall 2007) Why would lean body mass be lost with the fat mass? Simple: you are in a caloric deficit which means that you are not taking in enough calories to meet your needs to maintain your current bodily functioning, which includes maintaining lean body mass. If there is not enough energy coming in to maintain these tissues (lean muscle tissues, adipose cells, etc) then energy is taken from these tissues (these tissues are essentially stored energy) and used to provide for bodily functioning and physical activity.

*Personally, I would rather an individual eat enough calories to maintain adequate functioning (i.e. not a caloric deficit in dietary intake) and instead increase their energy expenditure (a caloric deficit due to increasing physical activity) for the purpose of maintaining lean body mass. This means a comparatively conservative daily caloric deficit, but with the potential to preserve lean body mass (muscle tone) in the long-term.

But the body responds to weight loss in a surprising way:

Metabolic adaptations arise during the process of weight loss including adaptive thermogenesis (slowed metabolism) and hormonal effects that favor decreased energy expenditure (limiting the amount of calories burned), decreased satiety and increased hunger. (Trexler, et al. 2014) Translation: when you try to lose weight, your body will adapt to prevent this from happening as a survival mechanism. This is a huge reason for difficulty in adhering to a weight loss diet, particularly if the diet itself is providing a large caloric deficit through restrictive eating AND increasing physical activity. (Trexler, et al. 2014) If there is too large of a caloric deficit (from both dieting/restricting AND increasing exercise) then the body does not have enough calories to meet its basic needs and it will slow metabolic processes (stop utilizing stored energy forms like fatty acids from adipose tissue) and instead store any energy coming in so that it BUILDS reserves. In this sense, with too low calories coming in, the body thinks it is starving, and will therefore slow down on burning fuel, and store everything it can as it does not know how long this starvation with last (how long until the next surplus).

**Think about it this way: the body wants to always be in balance, and when inducing weight loss, you are essentially disrupting that balance. Albeit this weight loss may be for the better in the long-run, but any change to the body's current state of homeostasis is going to be met with an adaptation in response like a slowed metabolism to limit large drops in body weight (lean body mass and fat mass as those are reserves for survival, and therefore your body does not want to lose them) AND a shift to CONSERVING energy intake (by increased storage) and promoting increased energy intake (through increased hunger and decreased satiety). (Trexler, et al. 2014) What does this mean? Dieting too hard (restricting too much/working out too much=too large of a caloric deficit) can lead to not only plateaus in weight loss, but weight gain and increased hunger.

What if I just want to eat less to lose weight and NOT increase activity?

For some, increasing physical activity may not be an option but there are successful weight loss diets known for caloric restriction. Caloric restriction however should not simply mean eating less total food, but rather ensuring appropriate amounts of protein and micronutrients (vitamins and minerals) while having a slight decrease in total energy (primarily from carbohydrates and fat). There has been a general acceptance in the scientific community that caloric restriction is associated with improvements in aging and longevity as well as body composition and weight-related health parameters. (Das, et al. 2017) In this recent study, a sample of non-obese adults (BMI 22-28, or 'normal to overweight') were randomized to either a diet that was less calories than their usual intake as recorded at baseline, or maintaining their usual caloric intake, for two years. (Das, et al. 2017) According to the results, the average calculated calorie intake at baseline (averaged between men and women) in this sample was approximately 2,400 calories whereby those who were randomized to the calorie restriction group were reportedly taking in an average of 300-400 calories LESS than this amount daily over the 2 year span of the trial. (Das, et al. 2017) **I would like to point out that this is considered a moderate caloric deficit in dietary intake, and where the newly reduced calorie intake sits right around the generally recommended 2,000 calorie per day guidelines. (Nix, 2013) As far as percentages of the macronutrients, the carbohydrate intakes were approximately 45% from total calories for both groups, dietary fat was approximately was 30-35% of total calories for both groups and protein intake was approximately 20% of total calories for both groups. (Das, et al. 2017) (It is important to note that the macronutrient ratios were similar for both groups with the only difference being the total amount of calories.) The calorie restricted group showed significantly greater weight loss, decreased waist circumference, increased fat loss, and increases in fat free mass where activity in the form of resistance exercise was the greatest predictor of increased fat free mass. (Das, et al. 2017) What does this imply? The group that was eating their usual intake was maintaining a caloric balance with their expenditure (i.e. not changing their body composition) but those who were in a caloric deficit (of 300-400 calories less in dietary intake per day) showed significant improvements in body composition (less body fat, more lean body mass) over the course of two years, particularly with the inclusion of resistance exercise being a predictor for lean mass gain (the addition of 'muscle tone').

But if a long-term moderate caloric deficit is good, than a short-term larger deficit is better, right?

Not exactly. Recall that there is a baseline threshold of energy intake needed to meet the demands of normal bodily functioning. If a caloric deficit (from diet and/or exercise) dips too low into this required amount, body processes shift from expending excess stored calories, to instead SAVING and storing calories. (Remember this as our innate and natural protection against starvation)**Burning through hundreds, or thousands of calories via exercise does not equate to actually LOSING those calories from stored energy (body fat)...

What about the low carb diets that everyone claims for weight loss?

The macronutrients (carbohydrates, dietary fat, and protein) should not be seen as optional, but rather essential in that maintaining appropriate intake of all three macronutrients is paramount to not only optimal functioning, but even basic survival. When it comes to the roles of the different macronutrients for weight loss, protein for example is specifically observed to have a positive influence on lean body mass during weight loss and can be associated with small increases in total daily energy expenditure due to the high thermic effect of digesting protein and its utilization in lean body mass. (Hall and Guo, 2017) While low carbohydrate diets are often popularized as effective weight loss diets, they also tend to be higher in protein than a usual dietary intake when not restricting carbohydrates. (Soenen, et al. 2012) In this study, a variety of macronutrient ratios were examined in an energy restricted diet for effects on weight loss and body weight maintenance, and not surprisingly, it was NOT the carbohydrate ratio that determined weight loss efficacy but rather the amount of protein in the diet. (Soenen, et al. 2012) In this study, the carbohydrate amounts ranged from 5% from calories (considered 'very low carbohydrate') to 25% from calories (considered 'low carbohydrate') to 50% from calories (considered 'high carbohydrate) and yet there was no difference in weight loss associated with carbohydrate content when protein was controlled for. (Soenen, et al. 2012) It was however, the differences in protein intake that were associated with weight loss effects where the relatively higher protein intakes (1.1g/kg body weight vs 0.7g/kg body weight in this study) were associated with weight loss and body weight maintenance over carbohydrate or fat content. (Soenen, et al. 2012)

The general idea behind a low carbohydrate diet is that by limiting dietary carbohydrates (glucose), that there is instead a greater reliance on utilizing fatty acids stored in adipose tissue for fuel. (Hall and Guo, 2017) While there can be short term weight loss effects observed in diets that restrict carbohydrates, studies suggest there is no significant difference between isocaloric diets that are either low fat or low carbohydrate with regards to weight loss. (Hall and Guo, 2017) In a meta-analysis of studies that looked at this difference between low fat or low carbohydrate weight loss diets, despite being the same caloric intake, the low fat diets (i.e. normal to high carb diets) showed significantly greater increases in fat loss and energy expenditure compared to the low carbohydrate diets. (Hall and Guo, 2017) This could be due to the notion that short term weight loss on a low carbohydrate diet is often due to loss of water, stored glycogen, and digestive bulk loss, thus equating to "quick weight loss", and then possibly followed by loss of body fat and lean body mass if calories are controlled for. The caveat to this however is the change in metabolism where after a prolonged period of inadequate carbohydrates for energy production (like from glycogen), the body is primarily relying on oxidizing fatty acids for fuel. As noted in the post on dietary fat, this does NOT specifically refer to utilizing stored body fat to oxidize fatty acids, but rather a more efficient ability to take the high amount of dietary fats coming in, and utilizing them for energy. **The short term weight loss effects of a low carbohydrate diet have been notably associated with aesthetic sports or weight category sports where there is a short time frame with which to reduce body weight, but only temporarily for competition (to make the weigh-in, etc). After this short-term weight cut, the athlete returns to a balanced intake of the macronutrients in order to maintain adequate functioning while training. In this respect, a low carbohydrate diet can be useful for those who utilize it properly, but not necessarily as a long-term diet or lifestyle to adhere to for generalized weight loss and health improvements.

What about eating several small meals throughout the day?

You have most likely heard this advice at some point with the explanation that small meals throughout the day would 'keep your metabolism burning'. While there is certainly merit behind this notion, there are some interesting study findings that question this theory.

Diet-induced thermogenesis is the notion that by taking calories in, you are stimulating thermogenic processes (the burning off of calories). With this thought in mind, there were findings to suggest that (relatively) higher energy intake was associated with increases in diet-induced thermogenesis compared to lower energy intake, higher protein and carbohydrate content was associated with greater diet-induced thermogenesis than just dietary fat, and interestingly consuming a meal as a single meal versus several smaller meals was associated with an increased diet-induced thermogenesis. (Quatela, et al. 2016) The notion that higher energy intake results in greater thermogenic effects should not be surprising as mentioned earlier, too much of a caloric deficit will transition the burning off of excess calories to instead storing as survival against starvation (i.e. slowing thermogenic processes). As was mentioned in the protein post, dietary protein is notably the highest (of the macronutrients) in terms of increasing thermogenesis which essentially means that simply digesting dietary protein 'burns more calories' (i.e. requires more fuel for metabolism) than digesting carbohydrates and fats.

One of the studies mentioned in the meta-analysis also showed significantly increased thermogenesis from metabolizing unprocessed foods compared to processed foods (multi-grain bread with real cheese vs. white bread with processed cheese product). (Quatela, et al. 2016) This could lend some support to the argument in favor of whole foods (that are high in fiber) versus processed or refined foods (that lack fiber).

However the most surprising result from this meta-analysis is the lack of support for several small meals instead of a few large meals in regards to increasing thermogenesis. (Quatela, et al. 2016) According to these studies, there were findings to suggest that eating a meal as one event significantly increased diet-induced thermogenesis compared to the same energy content spread out in multiple small meals. (Quatela, et al. 2016) If we look at this last point closely, this might make sense: a large meal would require greater effort to digest, thus increasing diet-induced thermogenesis. However, as many of us may know from experience, a large meal can also decrease your activity level (there is a preference for digesting food versus expending energy by physical activity). In this case, your physical activity would decrease and even your non-exercise movements (fidgeting, changing positions, moving around the room, etc) can decrease which could ultimately lead to less overall energy expenditure compared to eating smaller meals and maintaining physical activity and regular movement throughout the day.

What about intermittent fasting?

Intermittent fasting does NOT refer to the fasting associated with religious traditions, but rather purposeful ~16+ hour daily fasts followed by eating a day's worth of calories in a shorter (~8 hour) window of time. There are many claims for potential benefits of this pattern of eating yet a meta-analysis of recent study findings suggests that there is no difference in weight loss and maintenance between intermittent fasting caloric restriction and continual caloric restriction for overweight and obese participants. (Harvie and Howell, 2017) According to these results, caloric restriction with intermittent fasting was equally beneficial to just caloric restriction alone for weight loss in overweight and obese individuals, but where there is a lack of data for these associations in normal weight individuals. (Harvie and Howell, 2017) Some of the potential issues with this type of eating pattern is the fact that it can be variable based on interpretations. In some cases, this eating pattern may mimic a true fast with longer periods of fasting broken up with shorter windows of time with which to eat. There are theories that this type of fasting (with longer periods of fasting and shorter periods of eating) could be associated with binge eating, erratic eating patterns, heightened stress response, mood disturbances, and possibly influencing hormonal activity in women to where there is certainly a need for further research into this practice. (Harvie and Howell, 2017) *While there is definitely a need for more research in this area, a good rule of thumb would be to eat during your most active hours of the day.

Take from this what you will, but never stop learning.


Das S, Roberts S, Bhapkar M, et al. Body composition changes in the Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy (CALERIE)- 2 study: a 2-yr randomized controlled trial of calorie restriction in nonobese humans. American Journal of Clinical Nutrition. 2017; 105(4): 913-927.

Hadley M, Levine J. Endocrinology. 6th edition. Pearson Education. 2009

Hall K. What is the Required Energy Deficit per unit Weight Loss? International Journal of Obesity. 2007; 32(3): 573-576.

Hall K, Guo J. Obesity Energetics: Body Weight Regulation and the Effects of Diet Composition. Gastroenterology. 2017; 152(7): 1718-1727.

Harvie M, Howell A. Potential Benefits and Harms of Intermittent Energy Restriction and Intermittent Fasting Amongst Obese, Overweight, and Normal Weight Subjects:A Narrative Review of Human and Animal Evidence. Behavioral Science. 2017; 7(1):4.

Nix S. Williams' Basic Nutrition and Diet Therapy. 14th edition. Elsevier Mosby. St. Louis, MO. 2013.

Quatela A, Callister R, Patterson A, et al. The Energy Content and Composition of Meals Consumed After and Overnight Fast and Their Effects on Diet Induced Thermogenesis: A Systematic Review , Meta-Analyses, and Meta-Regressions. Nutrients. 2016; 8(11): 670.

Soenen S, Bonomi A, Lemmens S, et al. Relatively high-protein or 'low-carb' energy-restricted diets for body weight loss and body weight maintenance? Physiology and Behavior. 2012; 107(3): 374-380.

Trexler E, Smith-Ryan A, Norton L. Metabolic adaptation to weight loss: implications for the athlete. Journal of the International Society of Sports Nutrition. 2014; 11:7.

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