Introduction to Weight Loss and Weight Gain

If you have 30 seconds, read the summary
If you have 10 minutes, read the entire post.


  1. Energy balance is the relationship between energy in (food intake) and energy out (daily living)
  2. At its most basic level weight gain and weight loss happens through manipulation of the energy balance
  3. Note the distinct difference between weight loss and fat loss, between weight gain and muscle gain. At the end of the day, most people are aiming to gain muscle and lose fat. This may not always be the same in terms of weight though

Overload of information on this topic

Weight loss and weight gain appear to be a controversial topic with plethora of information we have available to us. Articles will list the top 10 foods NOT to eat and then there will be another one with ‘scientifically backed research’ that shows those same foods cause you to lose fat while you’re sleeping! It is probably fair to say that not all of the information out there is true. In my opinion, most of it is BS, some of it is taken out of context and only a small percentage appears to be accurate and correct given the current amount of information we have about the body. In order to dissect the amount of information out there I would like to outline a few concepts over the next few posts which will hopefully assist you in critically assessing the information for yourself. The first on the list is:

Energy Balance

Fundamentally, weight loss and weight gain is quite simple. Your body continuously uses energy to operate and to live. Every time you move, you are exerting energy in some shape or form, even during your sleep or when you’re in a coma your body will still consume energy to produce heat to keep your body warm. This energy use cannot continue indefinitely. We have to refill or replenish that energy somehow. This energy refill will predominantly come from the food we ingest during times which we might call ‘meals’ throughout the day. Notice that we are ALWAYS using energy, but only refilling energy (in the form of food) during certain times of the day. I personally like illustrating this in the example graph below:



Note that the horizontal axis on this graph represents the time or hour in the day and the vertical axis represents an arbitrary number for energy measured in units. Note that the most common measurements of energy are calories or kilojoules, however, for simplicity’s sake we have used a generic form of “energy units” here. This might be a typical example of a day for a layman or laywoman who likes to wake up at roughly 6-7am, walks to work, sits at the desk all day except for a short walk to clear their head during lunchtime, goes to the gym after work and then goes home to eat dinner and sleep.

In this particular scenario we can see that this person uses the same amount of energy as they refill i.e. Energy in = Energy Out. That’s great! However, the thing to point out is the issue I mentioned above where there is always energy usage, but not always sufficient energy refill. Take for example the Stone Age where hunters and gatherers might not have had the chance to eat 3 meals a day, they would have eaten a lot less frequently and it would not be uncommon for them to go days without food during winter for example. During this time when you are not refilling your energy, you cannot turn your energy usage ‘off’, your body is continuously running. This means that if you don’t eat enough, you may run out of energy which in this particular scenario would mean death. If only you knew that periods of shortages in food would come up from time to time, you would have stashed away some extra energy for days like these.

Fat as a safety net for under eating

The problem of possible famines in the future is dealt with through the concept of fat. This is one of the mechanisms which helped us survive in those dark stone ages. Fat is essentially a storage tool our body uses to set aside spare energy which we did not use and saves it for a rainy day. It is exactly like saving your monthly income so that unexpected expenses like a car crash will not cause you to file bankruptcy. In today’s society we often have lower energy consumption due to lack of exercises but higher energy refill in the form of higher energy food (ie. Sugar). Our body thinks we are eating a little extra to save us for the next famine which might never happen.

Below is an illustration of fat being used as a buffer so that we can continue operating despite the lack of energy intake. Note that this illustration spans over 2 days when in reality this process takes much longer than that.


On day 1 we are eating 140 units of energy but only using 110 units of energy, this gives us an additional 30 units of energy which we can store to be a backup in the form of fat.


On the second day, we aren’t able to eat enough energy. We ran out of eggs so we only had bacon and toast, we didn’t have enough money to buy the premium lunch so went for the sandwich and due to a stressful day at work we had little appetite at dinner. We subsequently under eat by 30 units of energy while maintaining the same energy usage. Luckily for us, we won’t die because we have our fat buffer built up from yesterday which we can draw upon to continue our daily activities.

A few notes on the above illustration

  • This is an oversimplification of the mechanics
  • Muscle could be broken down instead as our body is able to convert protein to energy (more on this in a later post)
  • Every single person will carry some form of fat. Stage ready bodybuilders have a body fat percentage of about 4-5% which means an 80kg competitor would still carry around 3.2 – 4kg of body fat. This is our safety net so that we don’t accidently starve ourselves to death.

Application to weight loss or weight gain

Generally speaking, weight gain and weight loss is usually attained through manipulation of our energy balance. Weight loss involves reducing the ‘Calories In’ part of the equation through eating less and/or increasing the ‘Calories out’ part of the equation through increasing exercise. The opposite is true if your goal is to gain weight. Now that we understand the concept of energy balance we can put things into context. In my experience a lot of the fitness advice or fad diets will in some way shape or form manipulate this equation:

  • The ‘No Carbohydrate Diet’ might work for someone who only eats steak and mashed potatoes for dinner because if they cut out the mashed potatoes, they are reducing their energy intake! Carbohydrates do not necessarily make you fat, but if you reduce your carbohydrate intake and do not replace it with anything else, then you are reducing your total daily energy intake. Diets that avoid sugar might also work, not because sugar makes you fat but it generally doesn’t have high satiety meaning that it doesn’t fill you up so you can eat a whole bucket of M&M’s (read: high energy) and still be hungry
  • The ‘Eat celery only’ diet might work for someone because celery is low in calories, so they are effectively reducing their energy intake
  • If your diet involves having to fast or not eat anything for 1 day of the week.. then you are reducing your total weekly energy intake!
  • Other advice like eat your veggies first before eating your main meal or drink a glass of water before your meal has the same purpose – to fill you up a little so that you cannot stuff your face when you get to your main meal. What does this do? Surprise surprise, it reduces energy intake!
  • Really skinny guys who are looking to put on weight will be advised to drink a lot of milk, not because milk inherently causes weight gain but rather because it is packed with calories while not being as filling as a vegetable equivalent for example. The person drinking milk may be able to ingest more calories per day this way

Relationship between fat, muscle and weight

We have talked about weight change but have made no distinction between fat/muscle. I mentioned above that muscle could also be broken down into energy if required, this means that:

  • Losing weight is slightly different to losing fat. Losing weight means that your total number on the scale went down, this loss could have been made up of fat and/or muscle
  • Gaining weight is also different to gaining muscle. Gaining weight means that your total number on the scale went up, but this gain could have been made up of fat and/or muscle


These things are not mutually exclusive and can happen at the same time. It is not uncommon to see what people call ‘body recomposition’ especially in new trainees where their bodyweight stays the same, but the individual has gained muscle and lost fat at the same time.

Our goal is of course to minimise fat gain when gaining weight and minimising muscle loss when losing weight. These will be discussed in a later post.

Now that we understand energy balance, we can talk about how to apply this knowledge to ourselves and set up our diet for our goals. This will be discussed in upcoming posts so stay tuned!



Toni is management consultant by day and an amateur powerlifter also by day.. he sleeps at night. He loves to strive for personal development and he achieves this through training, reading and maybe even writing.

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