by Bob Vandersluis

Ketogenic, Low Carb, Low Fat, Intermittent Fasting, the “diet” list goes on and on.  It’s hard to wade through the plethora of information on the numerous methods to optimize performance, and lose fat,

which is why we have done this for you!  


***All of the information that is summarized here comes from “International society of sports nutrition position stand: diets and body composition” by Aragon et al. 2017


This review is a snapshot of the massive amount of studies that have been done on the “diets” that have garnered the most attention and experts have deemed the most effective in terms of body composition goals.


First, lets discuss some of the major diet archetypes and define what they are.




Low energy diets (LED) are characterized by consuming 800-1200 kcal/day.  Very low energy diets are typically in liquid form and commercially prepared.  Even at protein intakes as low as 50g/day, lean mass loss from very low energy diets has been reported to be 25% of total weight loss, with 75% as fat loss.  Resistance training has shown an impressive ability to augment the preservation of muscle and even increase it during VLED, at least in untrained/obese subjects.




Low fat products are on the shelves of grocery stores everywhere.  The idea of consuming less of the most calorie dense nutrient has been a very novel concept since studies in the 1940’s came out about heart disease and were further investigated in the 1960’s, when the low fat diet really gained momentum.


Low fat diets have been defined as providing 20-35% fat, but it might be more accurate to call these types

of diets high carbohydrate.  Reducing the proportion of dietary fat can cause a reduction of total energy intake, thereby reducing body fat over time.  The premise f dietary fat reduction for weight loss is to target the most energy dense macro-nutrient to impose hypocaloric conditions.  However, over the long term, diets with lower energy density have not consistently yielded greater weight loss than energy restriction alone.




Low carb diets have been all the rage for decades now, and carbs have been demonized by so-called experts for no real reason.  However, there have been some benefits shown by restricting carbohydrates for a period of time in order to reduce weight.


There is no universal agreement on what quantitatively characterizes a low carb diet, but for the sake of the study, the percentage of total carbs in the diet is a maximum of 40%, or in absolute terms, less than 200g.  in comparing the effects of low fat diets to low carbs diets, studies have shown that there are no real differences in body weight or waist circumference, but did favor low carb diets for overall for fat mass loss and cardiovascular risk factors.  The authors speculate that the advantage of low carb diets over the control diets could have been due to their higher protein content.




Keto diets have been all the rage lately.  There are even pills out there that claim to instantly put someone into a state of ketosis by consuming ketones.  Numerous studies have shown many benefits to ketosis and some people have observed not only physical changes, but cognitive changes as well.


The Ketosis diet is objectively defined by its ability to elevate circulating ketone bodies measurably (ketosis).  Aside from completely fasting, this state is achieved by restricting carbohydrate intake to less than 50g, or 10% of total energy, while keeping protein moderate.

The proposed fat loss advantage of carbohydrate reduction beyond a mere reduction in total energy is based largely on insulin-mediated inhibition of lipolysis and presumably enhanced fat oxidation.


In the study, although insulin levels dropped rapidly, and substantially during Ketosis, an actual slowing of fat loss was seen during the first half of the keteogenic diet phase.  It has been postulated that the increase in ketone bodies produced impart a unique metabolic state, that in theory, outperforms a non Keto diet.  However, this claim is largely based on research involving higher protein intakes.

Increasing protein from 15-30% of total energy has been shown to result in a spontaneous energy intake drop by 441 kcal/day.  This led to bodyweight decrease of 4.9kg in 12 weeks.  Since protein has been shown to be the most satiating macronutrient,  this is not surprising.


In light of this, it has been concluded that the “special effects” of both low carb diets and ketogenic diets are not due to their alleged metabolic advantage, but their higher protein content.  


If there is any advantage to the ketogenic diet for fat loss, it is potentially in the realm of appetite regulation, which could be due to the increased satiety due to a suppression of ghrelin production.  (Ghrelin is a hormone which  is secreted primarily in the lining of the stomach. Ghrelin increases hunger).


Ketogenic diets suppress appetite more than low energy diets, but it remains unclear whether the appetite suppression is due to ketosis or other factors such as increased protein intake, or restriction of carbs.



High protein diets have been defined as intakes reaching or exceeding 25% of total energy.  Studies have shown that protein consumed at double the recommended daily allowance (RDA) (1.6g/kg) has repeatedly outperformed the RDA of 0.8g/kg for preserving lean mass and reducing fat mass.  More recent studies have shown dieting conditions involving high intensity interval sprints and resistance training, protein intake at 2.4g/kg caused lean mass gains and fat loss, while 1.2g/kg resulted in preservation of lean mass and less fat loss.  It has also been suggested that 2.3-3.1g/kg is appropriate for lean, resistance trained athletes in hypocaloric conditions.


Long term high protein intakes have demonstrated no adverse effects on a comprehensive list of measured clinical markers, including a complete metabolic panel and a blood lipid profile.


Of the macronutrients, protein has the highest thermic effect and is the most metabolically expensive.  Also, protein is the most satiating nutrient, followed by carbohydrate and fat being the least.





Intermittent fasting (IF) can be divided into three sub categories: alternate day fasting, whole-day fasting, and time restricted feeding.  The most extensively studied variant is alternate day fasting, which involves a 24hr fasting period, alternated with a 24hr feeding period.  Complete compensatory intake on the feeding days does not occur, and thus weight loss and fat loss occurs.

Whole day fasting involves 1-2 24hr periods throughout the week of otherwise maintenance intake to achieve an energy deficit.

Time restricted feeding typically involves a fasting period of 16-20 hours and a feeding period of 4-8 hrs.

The most comprehensive study to date on IF involved a comparison between intermittent energy restriction compared to continuous energy restriction.  They found that the two diet types resulted in apparently equivalent outcomes in terms of body weight reduction, and body composition change.  However, intermittent restriction was found to be superior in suppressing hunger, which may be attributed to the ketone production in the fasting phases.




To think that losing or gaining weight is as simple as “calories in” vs “calories out” is a bit naive.  There are many other factors at work including the behaviours that drive caloric intake, and the varying metabolic cost of processing macronutrients.  As an example, the thermic effect of protein is 25-30%, carbs 6-8%, and fats 2-3%.  There are also a variance in the thermic effect of some fats.  Medium chain have a significantly greater effect than long chain.  It has also been shown that within a mixed meal (50% protein, 40% carb, 10% fat) whey protein has a higher thermic effect than casein, which has a higher effect than soy.


Ultimately the interpretation of this and other data and the implementation of the procedures determines the progress made by people.  No single approach is ideal for all circumstances.




*Diets focused mainly on fat mass loss operate under the fundamental mechanism of a sustained caloric deficit


*Diets focused primarily on lean mass gain are likely optimized by a caloric surplus to facilitate anabolic processes and support increased training demands.


*A wide range of dietary approaches can be similarly effective for improving body composition, and this allows for a flexible program design.


*Increasing dietary protein levels to significantly beyond current recommendations for athletic populations may improve body composition


*Higher protein intakes (2.3-3.1g/kg) may be required to maximize muscle retention in lean, resistance trained athletes in hypocaloric conditions


*The long term success of the diet depends upon how effectively the mitigating factors of homeostatic drive are suppressed or circumvented


—Research has shown that resistance training and increased protein intake has circumvented the problem of adaptive thermogenesis, despite very low caloric intakes.