As discussed in this recent blog post, a calorie deficit isn’t the only factor to consider when you’re goal is to lose weight.

You see, we humans are complicated creatures.

My friend and I may eat the exact same diet (let’s assume we both weigh and train alike too), but that doesn’t automatically mean we’ll experience the same results.

One of the main reasons for variability in person to person progress?

Digestive function.

Your ‘digestive function’ refers to your body’s ability to effectively harness the energy from the food you eat, via absorbing the macro and micronutrients, and efficient expulsion of anything your body doesn’t need.

What Is ‘Digestion’ And How Does It Affect Weight Loss?

(Let’s make this simple. We’re briefly summarising the process so you’ve got the information you need to understand how to optimise your gut for fat loss; we aren’t preparing for a science test, so don’t stress!)

Digestion begins with the process of chewing, and the assistance of saliva whilst you’re enjoying a mouthful of (hopefully) healthy and nutritious food.

Upon swallowing, the ‘bolus’ (a term referencing the chewed up food item you’ve just consumed) will travel down your ‘oesophagus’ (think of this as a ‘food slide’).

From there your body will continue to digest the food you’ve eaten in your stomach, and will slowly (over the course of 1-4 hours) empty into the small intestine.

The ‘small’ intestine does a big job, processing and absorbing most of the nutrients within the meal over the course of another 4-8 hours.

From there, the food will process for another 12-25 hours in the various parts of the large intestine, before (finally), anything we don’t absorb gets *ahem* excreted.

So how exactly, is this process linked to weight loss?

The most obvious reason that a well functioning digestive system aids weight loss is that digestion uses calories.

That means that the whole process of eating the food to eventually absorbing what you can and excreting what you can’t… that takes energy.

And that means more calories burned, and an increased chance of fat loss.

This brings us back to our first point – not all calories are created equal. At least, from a digestive sense.

Clever scientists have calculated the amount of energy that processing every macronutrient takes.

And they found out it isn’t an even number by a long shot. The amount of calories burned in the actual process of digestion is referred to as the thermic effect of food or feeding (TEF).

Let’s say you eat 100 grams of protein. 20-30 grams of that hundred are going to be used in the actual processing of the macronutrient.

100 grams of carbohydrates? You’re only looking at 5-10 grams being burned in the digestive process.

And fats? That’s only going to be up to 3 grams (although don’t take that fact and run with the ‘fats are evil’ dogma- as always, there is more than one factor at play).

The Satiety Factor

Remember a few paragraphs back, where we discussed the stomach’s role of slowly dripping the eaten food into the small intestine? Well, this isn’t an unbiased process.

Certain macronutrients are going to be delivered at a faster rate than others – namely; carbohydrates will be processed first, followed by protein, fats, then fibre.

What does this digestion fact mean for your weight loss attempts?

If you want to feel fuller for longer (which you do), then a meal high in fibre, healthy fats and protein is going to fulfil that goal far more effectively than processed pasta or a sandwich. Even if the overall calories are exactly the same).

It’s worth noting that liquid meals and smaller particles are also processed a little faster, which is one of the benefits of whey protein shakes and liquid meals IF you need to absorb nutrients quickly (pre or post-training).

Although it could also be seen as a downside of powder supplementation if your goal is to remain satisfied for a longer period of time.

Intolerances And Other Factors That Affect Your Gut’s Functionality

As we’ve covered, the macronutrient breakdown of the calories you’re consuming makes a big difference in calories burned and food satisfaction via digestion.

But there are other factors that will affect the amount of the meals consumed you’re actually absorbing…

Food intolerances.

Food intolerances occur when an individual can’t absorb a particular food or its components (not to be confused with a food allergy – a far more serious issue).

The most common intolerances include dairy, eggs, yeast, wheat, gluten and soy.

The symptoms could be as simple as bloating or stomach upset, although they have a wide range of potential outcomes, including headaches and joint inflammation.

Suffice to say an intolerance will affect your performance while training and will decrease your body’s ability to burn calories and properly absorb the nutrients you’re providing it with. Making eating such foods a hindrance to your weight-loss aspirations.

Another common issue people face with their digestion is ‘leaky gut syndrome’, which can happen when the lining of the intestine becomes damaged or inflamed, disrupting the usual nutrient absorption.

This negative adaptation can cause similar symptoms to food intolerances, alongside possible nutrient deficiencies due to your intestine’s walls becoming inefficient at absorbing the nutrients you’re providing via your diet.

We discuss intolerances and leaky gut syndrome in more detail in this recent article if you want to learn more.

What About Gut Bacteria?

Another factor to consider is the complicated topic of gut bacteria.

Most people hear the term and assume all bacteria is evil, however, that isn’t the case; there are good-for-you bacteria living in your gut too.

The bacteria that inhabit our gut are referred to as ‘gut flora’ – and in general, are made up of a balance of both good (yay) and bad (boo) bacteria-guys.

An imbalance swaying towards the bad bacteria is called ‘Dysbiosis’.

Dysbiosis can eventually lead to IBS (irritable bowel syndrome), alongside various other less than pleasant symptoms such as; anxiety, skin issues, joint pain and infection.

The common causes of the imbalance would be through taking antibiotics, chronic stress and poor diet choices (which we’ll address shortly).

This gut flora imbalance can also lead to weight gain and definitely isn’t optimal for fat loss or performance.

How To Identify Gut Issues

There are two proven methods for identifying gut issues. Whether you have trouble digesting certain foods – we’ll start with the easier of the two.

The first step to identifying whether a particular food item is causing your digestive issues is to begin taking a food diary.

For every meal, write down how you felt before and after. If you start feeling any kind of discomfort, bloating or any other possible food-related symptom, write it down.

At the end of a two week period, you should be able to pick out patterns…

Feeling bloated the morning after a heavy pasta meal?

Knee’s hurting if you’re eating bagels for breakfast?

A particularly ‘interesting’ bathroom experience after you have milk in your protein shake?!

If you write everything down, patterns will emerge.

Once you think you’ve pinpointed an issue, take out the food in question and continue to take a food diary for another 2 weeks to see if the issue has subsided.

The second step, and on the more extreme end of the scale, you have the elimination diet.

This process involves you cutting out the following ‘main culprits’ from your eating for a period of 2-3 weeks:


  • Dairy
  • Eggs
  • Nuts & Seeds
  • Wheat & Gluten Containing Foods
  • Alcohol
  • Soy
  • Pork
  • Corn



(You can eliminate more, but these are the most common foods people have issues with)

After at least 2 weeks of absence from the aforementioned food groups, you’ll reintroduce a single item for one day.

For example, if you were to chose dairy, you could have milk with your breakfast and cheese with lunch and dinner.

Monitor how you feel on that day, and for 2 days afterwards (although those 2 days go back to avoiding dairy).

No symptoms? There’s a high likelihood you and dairy are friends and you can reintroduce it to your diet.

Now repeat the process with the other eliminated foods and see if you can identify any particular items that cause digestive stress.

Alternatively, taking a food intolerance test could help you know exactly what food you’re intolerant to and therefore which foods to eliminate, which would take out some of the ‘guess-work’ from the elimination diet phase.

Common Rules To Avoid Gut Issues

Whilst every person is different, there are a few golden rules that have been proven to benefit the function of your gut (and therefore aid your body composition goals):

  • Eat Slowly – rushing your food puts additional stress on your digestive system, relax and enjoy your food.
  • Ensure you’re consuming adequate amounts of iron. Deficiencies cause poor nutrient absorption in the gut. Foods that are high in iron include red meat, seafood, beans and dark leafy vegetables.
  • Get enough sunlight. Vitamin D is absorbed via getting some rays, and has the benefit of assisting in immune function and decreasing the possibility of gut issues.
  • Consume anti-inflammatory fats from foods such as wild-caught fish, grass-fed beef, flaxseeds and walnuts.
  • Avoid excessive sugar and alcohol consumption.
  • Pick real food over-processed. Our body is far more capable of absorbing what it has evolved to do so over thousands of years.
  • Eat foods high in probiotics, such as yoghurts, sauerkraut, kimchi, kombucha and kefir (if your digestion allows). Be especially diligent with this if you have to take antibiotics for any reason.

A healthy gut is an often-overlooked contributing factor to optimal health and maintaining a healthier gut will make weight loss much easier.

We hope you’ve found some useful information here to help you improve you digestive health if that’s what holding you back from achieving your optimal weight and health.

Digestive health health is something we explore with all of our valued clients here at Luke Bremner Fitness. We understand that health often begins in the gut and work closely with our clients to restore or optimise their gut health…

Which in turn makes weight loss and maintaining a healthy body so much easier downstream.

If you’re interested in working with our expert team to improve your health, you can learn more about our in-person personal training here and our online personal training here.