Diets And Body Composition


Many Diets, The Same Results

Many people want to improve their body composition. In other words, lose fat and retain (or even build up) as much muscle as possible. The result of this being a better looking body. Which I guess most of us want, right? When it comes to improving body composition, there are lots of diets out there claiming to be the next best thing. Honestly, no surprise in the fitness industry! Often, many people are left scratching their heads trying to figure out what sort of diet is actually the best to follow. Some, might even chop and change between diets in the hopes of finding the ‘one’.

Ultimately, none of this really helps you achieve your goals. All you do is waste valuable time, energy and motivation, which you could be using to fuel your weight loss efforts. The good news is, there really is no best diet for weight loss. They have all been found to produce weight loss to a similar extent. In fact, when it comes to the best weight loss diet, it really is all about the diet which provides you with the highest level of adherence. In other words, a diet which best allows you to stay on that weight loss path and reduces those compensatory effects (e.g. reduced satiety, increased appetite), which tend to lead to weight regain.

What Should A Weight Loss Diet Achieve?

There are two key things that your weight loss nutrition should help you to achieve: a drop in body fat and a retainment of your muscle tissue. If you are looking to improve your body composition, then achieving these two things will be your key to successful weight loss. Achieving one or the other, will leave you falling short of your ultimate goal. As a result, your nutrition should be looking to optimise your daily calorie intake, macronutrient composition and protein intake in order to get your closer to these two outcomes. The question is, what type of nutrition plan will help you best with this? Well, let’s take a look at what some of the scientific studies say.

Diet Type 1 (Low/Very Low-Energy Diets)

These diets are known as low-energy and very-low energy for a reason! They are usually characterised by daily intakes of ~800-1200 calories. So pretty severe! These diets are meant to induce rapid rates of weight loss (~1.0-2.5kg/week) while preserving as much muscle tissue as possible. They involve typically liquid calories meant to replace food and contain all the essential macro  (~70-100g/day C: 15g/day F and 30-80g/day P) and essential micronutrients needed.

A meta-analysis conducted by Tsai and Wadden (2006) investigated the short- (6 months) and long-term (1-5 years) weight loss effects of low-energy and very-low energy diets. In the short-term, very low-energy diets were found to provide significantly more weight loss  (~16% loss) than low-energy diets (~9.7% loss) in the short-term, while over the long-term, the extent of weight loss was very similar (5-6% loss). Moreover, most of the participants on either a very low- or low-energy diet were found to gain ~40-60% of their lost weight back. It was suggested that the large losses in weight experienced as a result of these diets, likely led to the up-regulation of various metabolic and behavioural compensatory mechanisms such as increases in appetite, behavioural fatigue, changes in peripheral and central hormones, as well as significant reductions in energy expenditures, leading to the large weight regain. Not great for those looking to keep off the weight in the long-term!

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Tsai and Wadden (2006). Figure shows the % difference in weight lost over the short-term for each group (VLCD – LCD). The mean difference was approx. 6.4% (highly significant) demonstrating the superiority of the very-low calorie diet (VLCD) over the low-calorie diet (LCD) in the short-term for weight loss. 

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Tsai and Wadden (2006). Figure shows the % difference in weight lost over the long-term for each group (VLCD – LCD). The mean difference between groupd was approx. 1.3% (not statistically significant). Both the VLCD and LCD provide similar levels of weight loss over the long-term. 

Diet Type 2 (Low-Fat Diets)

Low-fat diets are those in which ~20-25% of your daily calorie intake comes from fats. The rationale for low-fat diets comes from the fact that foods high in fat tend to also be the most energy-dense (highest in calorie content). It has been suggested that by reducing significantly the proportion of fat in your diet, it becomes easier to reduce total energy intake (calories) of which over time can increase potential fat loss.

In 2008, Saquib et al. investigated the effects of changes in dietary energy density (foods high in fat) on body weight in 2,718 breast cancer survival patients over a period of 4 years. Participants were split into two groups (control and intervention) with total energy intakes and physical activity levels not varying between both groups. The intervention group had significantly reduced their dietary energy density (decrease in % of energy derived from dietary fat) compared to those in the control group, and maintained it over 4 years. In the intervention group, these highly energy dense foods were replaced with a higher intake of fruits and vegetables. But, overall energy intake intake remained the same over the course of the study period. Within the control group, dietary energy density and diets remained relatively unchanged throughout the duration of the study.

After 4 years, the reductions in body weight observed between the control and intervention groups remained largely the same, despite the fact that the intervention group had replaced a large proportion of their dietary fats with fruits and vegetables. This suggested that large reductions in dietary fat alone will not independently influence weight loss results, if total calorie intake remains the same. Overall, this study showed that removing a large proportion of fat from your diet does not seem to be the answer for long-term weight loss. It would seem that changes in body weight are the result of reductions in total energy intake over time, and not through the removal of any single macronutrient group.  


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Saquib et al. (2008). Figure shows the changes in energy density, energy intake, physical activity and body weight of 2,718 cancer survivors over a 4 year study period. Total energy intakes and physical activity levels were similar between both the control and intervention groups. Energy density in the intervention group significantly reduced at both the 1 and 4 year study mark (high density fat foods replaced with lower density fruits/vegatables). However, even in the intervention group that replaced a large proportion of their fat for lower energy density foods, the levels of body weight were similar between groups after year 1 and 4. This suggested that changes in fat alone were not independantly reponsible for long-term weight loss promotion.  

Diet Type 3 (Ketogenic Diets)

When it comes to ketogenic diets, it’s usually those defined with ~ 10% (or > 50g) of daily energy derived from carbohydrates. This is typically the threshold point for inducing dietary (or nutritional) ketosis (an elevation in circulating ketone bodies). Protein is usually kept at around 1.2-1.5g/day with the rest coming from dietary fat (~ 60-80% of daily intake). Outside of pure calorie intake reduction, the benefits from dietary ketosis for fat loss are suggested to arise from enhanced fat oxidation and increased insulin-mediated inhibition of lipolysis.

The theory is that carbohydrates cause an increase in insulin secretion, of which this insulin subsequently results in the suppression of fatty acids being released into circulation (oxidation) and instead, directs them to fat storage (partitioning). Furthermore, if these fatty acids cannot be released into circulation, they cannot then become utilised by metabolically active tissues (such as the heart, liver and muscles). This is signalled as a form of cellular internal starvation and as a result, there is a reduction in energy expenditure (EE) and an increase in food intake. If this theory is to hold true, then there should be an increase in fat oxidation, an increase in body fat loss and, an increase in energy expenditure on a very low carbohydrate diet.

A study by Hall et al. (2016) investigated changes in fat mass and EE in 17 overweight/obese men over an 8-week study. In order to ensure adherence to the dietary protocols, all participants were confined to metabolic wards. In the first 4 weeks of the study, volunteers underwent a supervised high-carbohydrate baseline diet, followed by a 4 week isocaloric low-carbohydrate ketogenic diet with clamped protein. The daily calorie deficits managed on each diet were approx. 300 calories per day. Body composition changes were managed using dual X-ray absorptiometry. The participants spent 2 consecutive days each week in metabolic chambers in order to measure EE and respiratory quotients (RQ).

Hall et al found that within the last 2 weeks of the high-carbohydrate baseline diet, participants had lost an average of 0.5kg of fat. On transitioning to the ketogenic diet phase, there was an additional initial rapid decrease in body weight of approx 1.6kg. This was likely to be mostly from water losses since fat mass had only further decreased in this period by approx. 0.2kg. Over the entire 4 week ketogenic diet period, participants had lost a total weight of approx. 2.2kg with fat loss only being 0.5kg. The energy deficit throughout the entire two diet phases remained roughly around -300 calories per day.

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Hall et al. (2016). Figure shows the changes in bodyweight, body fat and energy balance over the course of the two dietary phases. Changes in body weight and body fat were very similar between the first phase (high-carbohydrate base line diet) and the second phase (ketogenic diet). The rapid decrease between days 0-15 represents the initial water losses as one transitions from the high-carbohydrate to ketogenic diet. However, after this, the rate in changes in body fat seem to decline. The extent of fat loss is very similar between both the high-carbohydrate and ketogenic diets. In C, the average calorie deficit was pretty similar between phases. This evidence goes against support for the carbohydrate-insulin model of fat loss in response to dietary ketogensis (which proposes increased fat oxdisation, utilisation and hence fat loss). 

It was further found that within the first week of the ketogenic diet phase, there was a slight, transient increase in EE of approx. 100 calories per day compared with the baseline diet phase. However, given that increases in nitrogen losses were reported in line with this transient increase in EE, increased mobilisation of amino acids from muscle (due to lack of carbohydrates) could have been responsible for this slight increase. Moreover, this increase significantly decreased in a linear fashion over the remaining course of the keto diet phase. Furthermore, RQ was found to significantly decrease from transitioning to the ketogenic phase from the baseline diet and remained roughly constant until the end of the study. This indicated a rapid and persistent increase in fat oxidation.

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Hall et al. (2016). Figure shows the changes in energy expenditure (EE) and respiratory quotients (RQ) over the course of the 8 week study. There is a slight bump in EE as one transitions from the high-carbohydrate to ketogenic diet. However, this rise is only transient and short lived. The increase could have occured due to increase amino acid utilisation in response to lower carbohydrates and/or higher levels of physical activity by volunteers on non chamber days. The increase is not enough to transfer to a significant metabolic advantage during ketosis. There is also a significant decrease in the RQ on transition into the ketogenic diet phase and this persists throughout the diet. This suggests an increase in fat oxidation.

The results of this study provided evidence against the carbohydrate-insulin model of fat loss. Although EE was found to increase slightly and only transiently, it would not have been enough to confer a strong enough metabolic advantage for fat loss. It is likely that any EE changes were due to the augmentation in utilisation of body protein and increases in activity levels of participants on days outside of the metabolic chamber. Moreover, the rate of fat loss had slowed after the first week of the ketogenic diet phase and remained almost unchanged from the baseline diet towards the end of the study.   

Diet Type 4 (High-Protein Diets)

High-protein diets are generally regarded as those in which protein intake reaches or exceeds 25% of total daily calorie intake. High-protein diets have been suggested to play a beneficial role in improving body composition. Interestingly, recent studies have shown that very-high protein intakes can produce significant changes in body fat mass and lean muscle mass over normal-protein diets.

A study by Antonio et al. (2015) investigated the effects of normal- (control) and high-protein diets on body compositional changes in 48 healthy, resistance trained men and women that undertook a heavy resistance training program.  The participants trained 5 days per week for an 8-week period. The high-protein group consumed 3.4g/kg, while the normal-protein group consumed 2.3g/kg.

Following the 8-week period, it was found that participants in the high-protein group had exhibited more significant reductions in fat mass (approx. 1.6kg) in comparison to those in the normal-protein group (approx. 0.3kg). Moreover, the body fat percentage reductions were roughly -2.4% for the high-protein group and -0.6% for the normal-protein group. Also, there was a significant increase in lean body mass for both groups of 1.5kg. What is also interesting is that the participants in the high-protein group increased significantly their total calorie intake by approx. 400 calories per day above baseline in comparison to the normal-protein group (100 calories per day).

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Antonio et al. (2015). Figure shows the changes in fat mass, body fat percentage and lean muscle mass in resistance-trained particpants following either a high-protein (approx. 3.4g/kg bodyweight) or normal-protein (2.3g/kg bodyweight) diet over a 8-week resistance training period. Those in the high-protein group exhibited exhibited the greatest reductions in body fat and body fat percentage, while both groups exhibited significant increase in lean muscle tissue (approx. 1.5kg). 

As suggested by Antonia et al. the greater decreases in fat mass in the high-protein group despite higher daily calorie intakes (400 vs 100) could be due to increases in daily sleep and resting energy expenditures. Higher protein intakes would likely raise these expenditures thus allowing for potentially more fat to be lost over time. This fat mass reduction might also be explained in terms of activity-related energy expenditure, of which has been shown to be positively correlated with weight gain. In other words, overfeeding would produce an increase in physical activity and thus energy expended during this activity. This might also explain the increase in fat mass reduction in response to high-protein.

Non-exercise activity thermogenesis (everything we do except sleeping, sports-like activity or eating) is also likely to shed light on the increase in fat mass loss in the high-protein group. This probably was higher in the high-protein group thus contributing to the higher levels of fat loss. Finally, the thermic effect of food should also be considered. Given that protein takes the most energy to break down and that carbohydrate/fat intake was unchanged between both diet groups, the higher-protein would have contributed to a larger thermic effect and thus potentially more fat loss over time.  It is certainly possible that a combination of these factors could be responsible for the enhanced body composition effects seen in the high-protein group.

Diet Type 5 (Intermittent Fasting)

There are many different variations of intermittent fasting: alternate-day fasting (ADF), whole-day fasting (WDF) and time-restricted feeding (TRF). In the fitness world, TRF seems to be gaining ground as a superior manner of improving body composition. TRF simply has you eating within a determined time window (feeding period), while fasting within the time outside of this (fasting period).

In a study by by Moro et al. (2016), changes in fat mass and fat free mass were investigated over an 8-week period in response to either a TRF protocol or normal-feeding (NF) protocol. In the TRF group, all participants consumed 100% of their energy needs within an 8-hour period each day, with their caloric intake divided into three meals (1.p.m, 4.p.m, 8.p.m). The remaining 16-hour period of the day was the fasting period. Participants in the NF group, consumed 100% of their daily energy intake into three separate meals (8.a.m, 1.p.m and 8.p.m). Calories and macronutrient distribution were matched between both groups. Fat mass and fat free mass were measured using dual energy X-ray absorptiometry.

After 8-weeks, there were significant reductions in fat mass observed in the TRF group in comparison with the NF group. However, levels of fat free mass were unchanged in both groups. Although it is not precisely known why (given similar calorie intakes and macro nutrients distributions) fat loss was greater in the TRF group, it is suggested that changes in mitochondrial biogenesis might be partly responsible. Blood sample collection and analysis revealed significantly higher levels of something known as adiponectin in the TRF group. It has been found that adiponectin can increase mitochondrial function, energy expenditures and fat loss. It is possible that increases in adiponectin in the TRF group favourably altered energy expenditures in some way leading to enhanced fat loss (although this was not tested in this study).

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Moro et al. (2016). Figure shows the changes in fat mass, fat free mass and adiponectin in those who followed the IF protocol and those who followed the normal diet protocol. After 8 weeks, there was a significant reduction in fat mass in the IF group, while fat free mass remaind almost unchanged in both dietary groups. The increase in adiponectin in the IF group is interesting because it highlights a possible mechanism (through changes in energy expenditures and mitochondrial function) by which the IF group lost body fat (even though calorie intakes and macronutrient distributions were very similar between groups). 

So Many Diets, They All Do Something!

In this article, I have summarized a select portion of the research on diets and their effects on body composition. Honestly, the topic is so huge that it would require me writing a book in order to compile all the research. However, one thing that we can be certain of from the above studies, is that all diets positively influence body composition in some way. Whether you are following a low-calorie, low-fat, ketogenic or high-protein diet, or even intermittent fasting principles, they all influence fat mass and fat free mass to some extent. But really, at the moment, there is no clear winner. As long as your energy intake (calories in/out) is adjusted to support your desired weight loss goals, then you will lose weight. No doubt about it. What is most important is that whatever diet you choose to follow, it allows you to see the weight loss process through. In other words, can you adhere to the chosen diet? After all, no matter how good or scientifically backed a diet is, if you cannot stick to it, then it will not work for you.

What is interesting from these studies is that other possible mechanisms of fat loss are starting to emerge that might help us to identify the efficacy of various weight loss diets. Although the basic principle of calories in and out is still the fundamental mechanism for ensuring successful weight loss, it might not be the only one at play. Especially given the above results observed in those people who followed a high-protein diet or an intermittent fasting protocol. Since the simple calories in/out principle cannot explain fully the results of these two studies, it is highly likely that additional mechanisms exist and come into play to influence fat loss. Even though more work still needs to be done to firmly establish what the precise mechanisms are, there is an idea that optimal fat loss might come from more than simply looking at calories in and out.


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