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Calorie Balance and the Biological Thermodynamics of Weight Loss


Calorie balance is the primary determinant of weight loss, and understanding how different diet approaches affect calorie balance is essential for long-term success. In simple terms, a calorie is a unit of energy that the body derives from the food we consume. When we eat more calories than our body requires for its daily functions and activities, the excess calories are stored as fat. To lose weight, one must create a calorie deficit, meaning the body must burn more calories than it consumes. All effective weight loss diets facilitate a calorie deficit through one mechanism or another (Hall et al., 2012). This essay will discuss various diet approaches, their mechanisms for producing calorie deficits, and the scientific evidence supporting their long-term effectiveness.

Direct Calorie Counting and Portion Control

Direct calorie counting and portion control involve consciously limiting the number of calories consumed by counting calories and controlling portion sizes. This approach allows individuals to create a calorie deficit and achieve weight loss (Johnston et al., 2014). However, studies have shown that calorie counting can lead to hunger and a sense of psychological deprivation, making it difficult to maintain in the long term (Lowe et al., 2013).

One of the reasons for increased hunger with calorie counting is the reduction in leptin, a hormone that regulates appetite and energy expenditure (Rosenbaum et al., 2010). When calorie intake is reduced, leptin levels drop, leading to increased hunger and decreased energy expenditure, which can make it difficult to maintain a calorie deficit. Additionally, calorie counting can lead to feelings of psychological deprivation, as individuals may perceive certain foods as off-limits, creating a sense of scarcity and increasing the likelihood of overeating (Herman & Polivy, 2008).

Low-Carbohydrate Diets and Ketosis

Low-carbohydrate diets, such as the Atkins and ketogenic diets, promote ketosis, a metabolic state in which the body burns fat for energy instead of carbohydrates. Ketosis can suppress appetite and reduce calorie intake, leading to weight loss (Gibson et al., 2015). Several studies have demonstrated that low-carbohydrate diets can be effective for short-term weight loss and improvements in blood lipid profiles (Bueno et al., 2013; Santos et al., 2012).

One of the reasons for appetite suppression in ketosis is the increased production of ketone bodies, such as beta-hydroxybutyrate, which have been shown to reduce hunger and ghrelin levels, a hormone that stimulates appetite (Stubbs et al., 2018). Furthermore, low-carbohydrate diets often result in a higher protein intake, which has been associated with increased satiety and reduced hunger (Leidy et al., 2015).

However, the restrictive food choices required by low-carbohydrate diets can make them challenging to maintain in the long term. A systematic review and meta-analysis found that adherence to low-carbohydrate diets declined over time, with many individuals returning to their previous eating habits (Hession et al., 2009). Moreover, concerns have been raised about the long-term safety of low-carbohydrate diets due to their potential effects on kidney function, bone health, and cardiovascular risk factors (Noto et al., 2013; Wycherley et al., 2012).

Calorie Density, Low-Fat Diets, and Long-Term Success

A more sustainable approach to weight loss might be to focus on the concept of calorie density. Calorie density is the number of calories per unit weight or volume of food, and consuming large volumes of low-calorie-density foods can cause stomach distension and suppress the hunger hormone ghrelin (Rolls et al., 2005). Low-fat diets are essentially low-calorie-density diets, as they emphasize the consumption of nutrient-dense, high-fiber foods such as fruits, vegetables, whole grains, and lean protein sources (Astrup et al., 2015).

The calorie densities of macronutrients play a significant role in weight management. Protein and carbohydrates provide 4 calories per gram, while fat provides 9 calories per gram. Consuming a diet high in protein and complex carbohydrates, with reduced fat content, can lead to a lower overall calorie intake and increased satiety (Paddon-Jones et al., 2008; Rolls et al., 2004).

Another factor to consider is the thermic effect of food, which refers to the energy required to digest, absorb, and metabolize nutrients. Protein has a higher thermic effect than carbohydrates and fat, meaning that a diet high in protein requires more energy for digestion, further contributing to a calorie deficit (Westerterp, 2004). Additionally, dietary fat is metabolized more efficiently than carbohydrates, with a lower proportion of energy expended during its conversion to body fat (Schutz, 2004). This makes a low-fat, high-carbohydrate diet more effective for long-term weight loss.

Population studies provide further support for the long-term success of low-fat diets. Countries in Asia, particularly Japan, have traditionally consumed low-fat, high-carbohydrate diets, and their populations have lower rates of obesity and obesity-related diseases compared to Western countries (Nakamura et al., 2004; Popkin, 2001). Moreover, no cultures throughout history have chosen to abandon carbohydrate consumption, suggesting that low-carb diets may not be a natural or sustainable way of eating.

Rapid Water Weight Loss and Low-Carb Diets

One of the reasons low-carb diets have gained popularity is the rapid water weight loss they can induce in the early stages (Jensen et al., 2018). When carbohydrates are restricted, glycogen stores in the muscles and liver are depleted, and water is released as a result (Kreitzman et al., 1992). This rapid water weight loss can lead people to believe that low-carb diets are more effective than they actually are in terms of actual fat loss.

In contrast, low-fat diets may not cause the same rapid water weight loss but are more effective at promoting long-term fat loss. A meta-analysis comparing low-carbohydrate and low-fat diets found that while low-carb diets resulted in greater short-term weight loss, the difference diminished over time, with no significant differences in weight loss after one year (Johnston et al., 2014). This highlights the importance of focusing on sustainable, long-term weight loss strategies rather than short-term results.

Challenges Americans Face in Adopting a Low-Fat Diet

The popularity of low-carbohydrate diets and the myths they create and perpetuate can make it challenging for Americans to adopt a low-fat diet. One major source of confusion is the fact that low-fat diets are high in carbohydrates, while low-carbohydrate diets are high in fat. This can lead to misconceptions about the roles of these macronutrients in weight loss and overall health.

Another challenge is the widespread belief that metabolic syndrome and insulin resistance are best managed with low-carbohydrate diets. While it is true that low-carb diets can improve glycemic control and insulin sensitivity in the short term (Gannon & Nuttall, 2004), it is important to recognize that the primary driver of metabolic syndrome is excess body weight, and the most effective treatment is weight loss, regardless of the diet approach used (Després et al., 2008).

A quote by Dr. John McDougall sums it up well: "The best diet for insulin resistance and diabetes is the best diet for weight loss, and that diet is low-fat, not low-carb." This statement emphasizes that weight loss, rather than macronutrient composition, is the key factor in managing insulin resistance and improving health outcomes.

One obstacle in adopting a low-fat diet is the effort required to learn new eating habits and meal planning strategies. However, this effort is worth it because low-fat diets are ultimately more human and livable than highly restrictive low-carb diets. By focusing on nutrient-dense, high-fiber, low-fat foods, individuals can enjoy a wide variety of satisfying meals that promote long-term weight loss and overall health.


While all diets can be effective for short-term weight loss, low-calorie-density diets, or low-fat diets, appear to offer the most sustainable and effective approach for long-term success. The scientific evidence supports the notion that low-fat diets are more in line with traditional eating patterns and are more effective in promoting long-term weight loss and health improvements. By focusing on consuming nutrient-dense, low-calorie foods and reducing dietary fat, individuals can create a calorie deficit without experiencing excessive hunger or feeling deprived. This approach is more sustainable, natural, and aligned with the way humans have historically eaten, making it the ideal strategy for lasting weight loss and improved health.

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