Do I Cut Carbs Or Fat For Weight Loss?

Tom Price by Tom Price

Is cutting carbohydrates or fats the most effective for fat loss? Or are there other factors at play when choosing a weight loss strategy? Find the answer to these questions and more below

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Do I Cut Carbs Or Fat For Weight Loss?


The internet, particularly social media, is a confusing place with an abundance of misinformation regarding weight loss. As a population with strong desires to get lean and muscular, we're constant targets for this misinformation which more often than not, promotes a definitive link between weight loss and restricting either carbohydrates or fat. But is one better than the other? And how do you incorporate this in a way that supports your body, promotes fat loss, and satisfies your lifestyle and taste preferences? Let’s discuss.


A study worth reading


If there is one thing you take away from this article it's this: as long as you are consistently in a calorie deficit with an adequate amount of protein, it's likely that you will lose weight and conserve some of your muscle. 


One study which illustrated this was The DIETFITS Randomised Clinical Trial published in 2018. The study focussed on 609 clinically overweight or obese males and females between the ages of 18 and 50. Half were assigned a 'healthy' low fat diet while the other half ate a 'healthy' low carbohydrate diet, both of which consisted of just over 20% of calories from protein. More general instructions were given to "1. maximize vegetable intake; 2. minimize intake of added sugars, refined flours, and trans fats; and 3. focus on whole foods that were minimally processed, nutrient dense, and prepared at home whenever possible." (1) Coincidentally, despite participants not being provided with any total daily energy targets, they achieved a 500-600 calorie per day deficit (on average).


So what happened? After 12 months, both groups lost the same amount of total weight (5.3kg for low fat group and 6kg for low carbohydrate group) with similar declines in body fat percentage and waist circumference. This meant that their weight loss was independent of how low in fat or carbohydrates their diets were. The following factors most likely contributed to weight loss:



a. Achieving a slight calorie deficit - A negative energy balance allows the body to turn to fat oxidation for energy so that it exceeds fat deposition. Only a slight deficit is needed to access fat stores as energy is still needed to support daily vital functions related to basal metabolic rate (energy needed for your organs and processes which keep you alive), thermic effect of food (energy used to consume, digest and absorb the food you eat), and non-exercise activity thermogenesis (incidental physical activity such as cleaning, making the bed, walking to the toilet etc.). 

Decreasing calories too much means your body may potentially shut off 'less essential' systems as energy is reserved for those which are more imperative for survival. An example of this is REDS (relative energy deficiency in sport) where energy availability is so low that reproductive organs shut down and bone density declines. 


b. Consuming adequate protein - Although not a major focus of this study, it is still important to touch on. Protein is the most satiating macronutrient (along with fibre), meaning participants required less food to feel full. Furthermore, the energy needed to actually break protein down into amino acids is quite high, contributing to an increase in the thermic effect of food (a form of energy expenditure).  


c. Consistency - The weekend accounts for nearly 30% of your week, so dropping the ball here will be counterproductive to your goals. Slow, consistent weight loss is achieved through staying with your strategies consistently rather than allowing yourself to slide into poor eating behaviours on a regular basis. (2,3) 


d. Increased fruit and vegetable intake - Adherence to the instructions given was high among most of the participants, most likely contributing to their successful weight loss. Apart from having a great vitamin, mineral and antioxidant profile, fruit and vegetables contain high amounts of fibre while being low in calories. Because the vast majority of fibre isn't even digested by the body and is highly satiating, it keeps us full and inhibits excess calorie intake all having a high thermic effect of food. By focussing on consuming more fruits and vegetables, there is less room to squeeze in high calorie foods which offer close to no nutritional benefits. Like protein, fibre has a high thermic effect of food.



Which one is right for me?


 Choosing diet strategies is best done with an Accredited Practising Dietitian. Diet is not a one size fits all approach because everyone is different. Ultimately, it depends on what diet supports your lifestyle, the foods you like, and your training regime. One thing that is agreed on across the board in the dietetic community is that fat loss is linked to eating a well-balanced diet consisting of adequate protein, fibre, fruit and vegetables with low intakes of sugar, salt and saturated and trans fats.  


From the perspective of fat and carbohydrate intake, working out which is right for you will involve a bit of trial and error - so make an initial decision based on what foods you like to eat (and the ones you can do without), what you enjoy eating, and your daily lifestyle. Working alongside an Accredited Practising Dietitian should be at the top of the list of priorities as they will be able to help navigate the infinite number of food combinations to find the one/s which suit you.


Generally speaking, for an average healthy individual, try and stick with one so you can get the feel of what to cook and how it makes you feel physically and mentally. If you find it isn't conducive to your lifestyle, the foods you like, or training needs then try the other. It can also be a good strategy to swap between the two during the day or week while making sure to maintain a calorie deficit. Depending on the extent of the deficit, the necessary protein intake may surpass the recommended 1.6-2.2 g/kg for athletes (4,5). If you're an athlete, having a “food for performance” mindset is highly desirable. There is a fine line between being in a calorie deficit (which will help you lose weight) and sacrificing the quality of your training sessions. Eating appropriately to support these activities while maintaining a deficit created not only by slightly restricting calories, but increasing energy expenditure through your training will ensure you're still driving physiological adaptions which will improve your performance long term. 


If you're wanting to alternate between the two, it’s best to keep your low carbohydrate meals as far away from physical activity as you can while pulling those higher carbohydrate meals in closer to fuel and replenish your energy stores (i.e. glycogen). Below is an example of what a typical day might look like for a healthy individual wishing to lose weight and alternate low fat and low carbohydrate meals. Keep in mind that serving sizes and the number of meals vary for people depending on their age, gender, body composition, activity levels, lifestyle and genetics:


  • Breakfast - 3 egg omelette with grated cheddar cheese, cherry tomatoes and 1/4 avocado Low carbohydrate

  • Pre-Training - Low fat Greek yoghurt, 1 banana and 1/2 cup quick oats Low fat

  • Post-Training - 100g grilled skinless chicken breast or 170g marinated tofu, asparagus, sweet potato mash (using only a splash of low fat milk, salt and pepper) Low fat

  • Dinner - 80g lean beef steak, side salad with lettuce, tomato and cucumber, olive oil based salad dressing Low carbohydrate

  • Snack - 1 Scoop True NIGHT85, 30g (small handful) unsalted nuts of choice Low carbohydrate


How to track fat loss


The decision to lose weight should be accompanied by good reasoning (such as to assist or improve performance, or part of a prevention plan agreed on by medical professionals), followed by setting some goals. Head over to How To Set Fitness Goals That Actually Work for some useful tips. In a nutshell, it explains the notion of setting measurable behaviour based goals which assist in paving the path to the desired outcome. A great example used is eating until 80% full at each meal (the behaviour goal) to achieve 5kg weight loss (the outcome goal). 


Now that you have set some goals, you need to consistently track your progress to make sure you're on the right track. The great thing about this is that if you're tracking progress on a weekly basis and find that your strategies aren't working, you have a reference point to investigate further into what might need changing. 


As far as fat loss goes, there is an abundance of methods to measure it, some of which are much more accurate than others. Things to consider when deciding on a tracking method are accessibility, cost, and accuracy. 


1. DEXA Scan - The' gold standard' of body composition measurements is the DEXA scan (dual energy X-ray absorptiometry) due to it's accuracy and reproducibility. Basically, it takes an X-ray of your body and produces data on bone mineral density, fat free mass and fat mass. The downside is that most people either cannot afford this expensive exercise nor do they have easy access to a machine.


2. Bioelectrical Impedance Scale - A slightly less accurate (but much less expensive) method which sends a weak electrical current through the body, measuring total body water. The machine then converts body water into fat free mass giving you an idea of how lean you are. This method is known to be relatively accurate (provided you aren’t ridiculously over or underhydrated) and quite low cost at around $25 per round in some gyms.


3. Skin Folds - Is a manual process involving having a professional use callipers to measure subcutaneous fat (fat under the skin) in several areas around the body. Since subcutaneous fat is what you're trying to lose, this is a great method of tracking the specific goal. If you're wanting to hit two birds with one stone, you can organise to see an Accredited Practising Dietitian who will take skin folds for you and provide you with personalised nutrition advise. Having the same professional with the same callipers take measurements each time is important to maintain consistency and therefore accuracy. 


4. Scales - The least recommended method to track your progress as it only measures total body weight (which is the sum of bone, muscle, all fat, water and organs). What the scales say might be misleading, especially if your carbohydrate intake is suddenly decreased. After periods of low carbohydrate intake, glycogen is depleted and along with this, stored water (or 'water weight') is lost. While this is great for weight making sports, somebody just wanting to lose fat mass may think they have done just that when in fact it is just water and glycogen that has been lost. In addition, constantly checking the scales can lead to body dysmorphia and disordered eating which is counterproductive to overall health. Nonetheless, checking the scales once per week and graphing it over a period of weeks is cheap and can be a good indicator of consistent weight loss.



How much weight should I be losing?


There is no one size fits all and the rate of weight loss depends on a variety of factors which are completely individual. Generally speaking, 0.5-1kg per week is a good ballpark to be aiming for, with evidence suggesting that slow, consistent weight loss which can be maintained over a long period is the way to go (5,6). 




The struggle of navigating the vast array of misleading nutrition information is something we can all identify with. Although it is important to maintain a slight calorie deficit with a protein intake of 1.6-2.2g/kg of body weight (or more), keeping it simple and adapting meals to your needs at the time is a must. 


As for decreasing carbs or fats - does it matter? No. This is your choice and all part of fitting in with these wants and needs. Consistency in meal planning, training and tracking goals is what matters.


  1. Gardner, C.D., Trepanowski, J.F., Del Gobbo, L.C. et al. (2018). Effect of Low-Fat vs Low-Carbohydrate Diet on 12-Month Weight Loss in Overweight Adults and the Association With Genotype Pattern or Insulin Secretion. The DIETFITS Randomized Clinical Trial. JAMA. 319(7), 667-679.
  2. Gorin, A.A., Phelan, S., Wing, R.R., Hill, J.O. (2004). Promoting Long-Term Weight Control: Does Dieting Consistency Matter? International Journal of Obesity Related Metabolism Disorders. 28(2), 278-281.
  3. Wing, R.R., Phelan, S. (2005). Long-term weight loss maintenance. The American Journal of Clinical Nutrition. 81(1), 222S-225S.
  4. Hector, A.J., Phillips, S.M. (2018). Protein Recommendations for Weight Loss in Elite Athletes: A Focus on Body Composition and Performance. International Journal of Obesity Related Metabolism Disorders. 28(2), 170-177.
  5. Longland, T.M., Oikawa, S.Y., Mitchell, C.J. et al. (2016).Higher compared with lower dietary protein during an energy deficit combined with intense exercise promotes greater lean mass gain and fat mass loss: a randomized trial. The American Journal of Clinical Nutrition. 103(3), 738-746.
  6. Ashtary-Larky, D., Ghanavati, M., Lamuchi-Deli, N. (2017). Rapid Weight Loss vs. Slow Weight Loss: Which is More Effective on Body Composition and Metabolic Risk Factors?. International Journal of Endocrinology and metabolism. 15(3), e13249.

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IMPORTANT INFORMATION: all content provided here is of a general nature only and is not a substitute for individualised professional medical advice, diagnosis or treatment and reliance should not be placed on it. For personalised medical or nutrition advice, please make an appointment with your doctor, dietitian or qualified health care professional.

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