Key Topics Covered

Today’s podcast explores the idea that being in a calorie surplus leads to consistent size gain, while a calorie deficit results in size loss over time. However, individual responses to these conditions can vary. We’ll start with the “7,700kcal rule,” which states that 1kg of body fat equals 7,700kcal and about 1,200kcal is needed to build 1kg of muscle. For example, a 500kcal daily deficit could theoretically result in half a kilogram of fat loss per week. While this rule offers a general guideline, we’ll discuss the individual variations that influence these outcomes.


Part 1 – The Theory

  • When you change your habitual energy/calorie intake – there are inherent changes to calorie output, through several mechanisms:
  • BMR – This is our “metabolism” which adapts in accordance with habitual calorie consumption.
  • You may have heard us talk about this previously in regards to metabolic adaption – food increases = extra calorie output through an up regulation in certain bodily functions and on the flip side less calories = reduced calorie output through down regulation.
  • How much your intake changes your total daily BMR will depend on the size of the surplus/deficit, the length of the phase & genetics.

Changes in intake can lead to changes in BMR, NEAT, EAT and Thermic effect of food:

  • Basal Metabolic Rate (BMR) = The rate of energy expenditure of an individual at rest.
  • Thermic Effect of Food (TEF) = The amount of energy it takes for an individual to digest, absorb and metabolise food.
  • Non-exercise Activity Thermogenesis (NEAT) = Incidental movement e.g. For someone who is in a calorie surplus or has increased their calorie consumption, they will have more energy for example, even fidgeting. Whereas, someone in a deficit will most likely have less energy and engage in less incidental movement.
  • Exercise Activity Thermogenesis (EAT) = Formal exercise e.g. Maybe you train less on a deficit or you may start exercising more efficiently in a surplus but you may burn fewer calories for the same exercise.

Part 2 – The Theory

  • Absorption of food can change
  • Differences based on muscle vs fat gain e.g. the different caloric values.
  • Adherence to the plan can change
  • It’s also worth acknowledging that the adherence issue makes it hard to assess this in the real world.

Part 1 – What We See In Research

  • I’m going to use one study as an example (linked in show notes).
  • The had 24 participants
  • They overfed them for 84 days by 1000kcals per day (technically it was a 100-day study with every 7th day at maintenance)
  • They did a maintenance phase leading into the study to confirm that it was ~1000kcal surplus.
  • All exercise was standardised to a 30-minute walk per day for everybody.
  • The average gain was 8.1kg
  • Somebody gained as much as 13.3kg and somebody else only gained 4.3kg
  • Assuming a decent level of compliance, this study highlights how differently each person may respond to a surplus/deficit even if it is theoretically the same size deficit/surplus.

Part 2 – What We See In Research

  • That’s a crazy difference.
  • For context the theoretical combined total surplus was 84,000 calories.
  • If that 13.3kg was 100% body fat, it would require just over 100,000kcal due to the 7,700kcal rule.
  • So this therefore means that if the maths was perfect, that person must have had NO increase in energy expenditure (or even a small drop) AND gained some weight in non-fat form e.g. muscle, glycogen, food weight, water etc.
  • Potentially the maths wasn’t perfect e.g. they were already in a small surplus at the start of the study.
    Anyway – the person who gained only 4.4kg clearly had a huge increase in calorie expenditure and/or a decrease in calorie absorption.

Further Interpretations of the Research

  • That’s just one study with a small sample size.
  • But it’s safe to say that there is a huge variation in responses, particularly when factoring in how we respond in other ways
    for example, one person’s appetite might change more than another.
  • Finding research on this topic is a bit harder than you’d think.
  • Theoretically there is a LOT of research out there since we can look at any controlled study with a surplus or deficit, but it’s hard to find compilations with useful data.

What Do We See in Practice?

  • While we clearly see this in practice, it is borderline worth ignoring what we see in practice.
  • We know that self-reported data is very unreliable.
  • If somebody seems to be an outlier, are they an outlier or is their reporting just off? We can still work very effectively with them,
  • we would be hesitant to rely on that data.

Summary


There is a clear difference in how each individual responds to a deficit or surplus. However, with that said, this doesn’t break the calories in, calories out model, it is just part of the model. So rather than thinking about it in a very simplistic form, this equation is highly complex with many many moving parts.

Relevant Blogs/Research

Relevant studies: