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  • Writer's pictureScott Murray

i ate a big mac a day for a week...

SO... This week I ate a Big Mac a day in the name of science in the hopes of proving to you once and for all that foods don't make you fat, CALORIES do!

As always, if you are reading this then you have likely come from my recent “I ate a BigMac every day for a week” video, in which case, go back and smash the like button and be sure to share it with all your friends and family (srs)… Let’s make it go viral… #chances lol

Anyway, as I said in the video, this blog post is going to give you a quick rundown of the energy balance science and how it was possible for me to fit a BigMac, a quote on quote “dirty” food, into my diet for a whole week and not gain weight (in fact I lost it). That, along with actual screenshots of each day’s energy expenditure and total macros during the week to show you exactly how the two matched up and hopefully further explain the science I reference below.


To start, I’d like to quote a highly beneficial segment from a paper by Hill, Wyatt & Peters (2012) who state that:

The 3 main components of energy balance include energy in (EI), energy out (EO) and energy storage. Weight can only change when EI is more/less than EO over a chronic period of time. EI comes from food/drink i.e. protein, carbs, fat and alcohol vs EO which comes from resting metabolic rate (RMR), thermic effect of food (TEF) and the energy expended through both FORMAL and informal activity e.g. Lifting or NEAT.

· The more lean body mass and fat mass you carry, the higher your RMR will be.

· Similarly, the more you eat, the higher your total TEF will be.

· Finally, the more active you are (NEAT and formal activity) the more energy you will expend thus considered the largest variable component of energy expenditure.

Regardless of the above, when EI = EO, the body is in energy balance where body weight remains stable. However, when EI > EO, a state of positive energy balance occurs and the consequence is an increase in weight, 60-80% of which is usually fat. Conversely, when EO > EI, a state of negative energy balance arises and the consequence is a loss of weight (again with 60 to 80 percent from fat).

Therefore, person A (70kg) may be very physically active and maintain their weight by eating and expending 3,000kcal/day as opposed to person B (70kg) who adopts a more sedentary lifestyle and maintains the SAME weight BUT by eating and expending only 2,000kcal/day. However, if Person B failed to sufficiently reduce their EI to match a reduced EO, over time, they would gain weight as they’d be in a daily 1000kcal surplus.

What am I trying to get at? CALORIES! I know that in terms of “the gym”, there are a plethora of variables that can influence gaining/preserving muscle, gaining/losing fat etc. such as protein intake (Helms et al 2013), lifting (Bryner et al 1999), supplementation (Kreider et al 2003) etc. However, it’s still clear that everything still all comes down to CALORIES.

· When in a surplus, you’re going to GAIN both muscle and fat.

· When in a deficit you’re going to LOSE both muscle and fat.

Therefore, if you’re looking to alter your body composition the first step you need to take is to track those CALORIES and then worry about the following (in order of importance)

1. Macros

2. Micros

3. meal timing

4. Supplements

THIS is why I did not gain weight from eating BigMacs all week. As you will see below, my overall expenditure matched my intake and thus, as above EI = EO yielding no scale weight loss/gain, REGARDLESS of the fact that the food TYPE eaten was of “poorer quality”.

This then leads me onto the next question that I know you will ask. What about macros/micros and the different thermic effects they have? Surely if you were to have replaced the BigMac with a higher protein, lower fat “whole food” you would have seen better body compositional changes?

Correct, as far as the literature goes, it’s quite clear that the degree of processing between refined, process foods and whole foods can influence their CALORIC value and, although this may be me nit-picking, processed foods (much like a BigMac) have shown to takes less energy to digest and absorb compared to whole foods (Barr and Wright 2010). Therefore, 500kcal of processed food could “technically” end up being more NET calories (calories left over after taking into account the thermic effect of food) than 500kcal of whole food. Ok but why is this useful?

It’s useful because, in terms of NET calories (still greatly nit-picking), if processed foods result in more NET calories, a dieter would therefore benefit more from a diet rich in whole foods in order to maximise the degree of TEF and end up with less NET calories than if eating junk. It’s almost like “boosting your deficit”. On the other hand, one could argue that, if bulking and struggling to gain weight, you would thus benefit more from a mostly processed food diet to maximise having LESS NET calories lol. That being said however, as I will discuss below, that is definitely not advisable from a health and performance standpoint.

Furthermore, revolving most of your foods around “whole foods” will make dieting (regardless of bulking or cutting) easier to adhere to, especially as far as satiety goes. This is because, especially when dieting, research consistently shows increases in the “hunger hormone” ghrelin (Rossow et al 2013) and decreases in the “satiety hormone” leptin (Hagmar et al 2013). Thus, by opting for more voluminous, high fibre, protein rich foods during a fat loss phase, as opposed to highly refined carbs and fats (like a BigMac), you would feel more satiated during the day and thus be less likely to throwing the towel on your calorie deficit.

So, whole foods are great and should be what you revolve the majority of your diet around but not ALL of it.

Correct, although I am a huge advocate of a mostly whole food diet, the above still doesn’t debunk the energy balance equation and that you can still follow a more IIFYM plan and lose weight eating BigMacs at every meal.

There is even a documentary on it –

Along with my man Jorday Syat’s 30 day experiment -

Anyway, back to IIFYM and fitting in junk food to still lose weight.

For those unaware, IIFYM is a dietary strategy based on the idea that as long as what you eat “fits your macros” (protein, carbs and fats) it’s okay to eat it. While from a scientific standpoint this method is supported by the above energy balance equation, it still doesn’t then mean that IIFYM is a free pass to eat junk all day to simply “hit your macros”.

Regardless of if wanting to lose or gain weight, you should STILL be including whole foods in your diet.

Correct, IIFYM is no different to any other diet. It should be a diet with healthy, micro dense foods as its FOUNDATION (80%+) however where IIFYM differs from other diets is that you have

a) The OPTION to vary your intake of what healthy foods you eat as much as you want

b) You ALSO have the OPTION to include the odd treat (like a BigMac).

This is then why it’s so successful as a long term diet as, unlike 100% rigid dieting strategies which have you eliminate foods/food groups, having that added OPTION eliminates the irrational obsession that come from only being ABLE to eat healthy foods along with eliminating the development of binge like eating behaviours (Stewart et al 2002).

As much as you may not want to hear it, although great and highly effective (short term), 100% rigid “clean eating” diets are NOT sustainable, they’re socially isolating, mentally exhausting, unnecessarily stressful & scientifically proven to result in the highest rates of diet failure (Pelchat and Schaeffer 2000, Smith et al 1999, Stotland 2002, Meule et al 2010). Therefore, much like you saw from the video, my BigMac, or in most cases my cereal and icecream macro cappers at night are my “treats” for the day. I mean, at 500 calories, a BigMac was a minor ~10% of my total caloric intake, the rest of which was coming from whole foods. The result? A diet that

· Reaps all the benefits of whole foods mentioned above.

· Reaps the benefits of IIFYM mentioned above.

· All while staying true to the energy balance equation thus allowing me to still manipulate my body composition according to how I want to.

It’s a win win

Anyway, you know me, I could go on forever about other aspects in more detail however, that is my usual 2.5 hours of writing and researching done for you for today so please do feel free to message me if you have any more specific questions about food types, energy balance etc.

However, the take-home message is that, overall as long as your calories are in check, regardless of the type of food you eat, you will lose weight, if in a deficit. Is it good for your health to eat like a slob all day and still maintain your weight? No, but it’s POSSIBLE if you simply manipulate the energy balance equation to your favour, that’s all I’m trying to get at here, otherwise you know by now that I still highly advocate a mostly whole food diet.

Nonetheless, below are my 7 days’ worth of expenditure vs intake to give you more of an insight into the week and how the energy balance equation worked out for me.

As always, don’t forget to like and share this on your socials and that, if you’ve read this far, I really do appreciate you so much, your support means the world.


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