“Carbs Make You Fat” & Other Common Carbohydrate Myths Debunked

“Carbs make you fat”

Carbohydrates can make you fat the same way as protein and fat can make you fat; by consuming too much.  Research has shown that regardless of where you get your calories from, as long as you are in a calorie deficit then weight loss will ensue.  In one particular study, that was true for diets containing around 15% calories from carbohydrate, as well as 85% calories from carbohydrate [1].  Although there may be something to be said for diets higher in protein showing a great benefit to fat loss, the ratio of carbohydrate to fat seems less important [2].

In summary, consuming a high proportion of your calories from carbohydrate will not make you fat unless you are consuming more calories overall than you are expending.

“No carbs after 6pm if you want to get lean”

I’m not sure who would want to live in a world devoid of carbs after 6pm, however I have heard this myth propagated so many times it’s no surprise people believe it as true.  Drawing on the answer above, only excess calories will make you fat, not what macronutrients they come from or when you choose to consumer them.

However there is more evidence to debunk this myth.  Research has shown that consuming carbohydrates at night as part of a calorie deficient diet, may actually provide more benefits to weight loss and hormone regulation than a standard weight loss diet [3].

Further to this, other research has shown that calorie restricted diets incorporating intermittent fasting (fasting for large periods of time and consuming calories in a shorter time period) may have added benefits to a normal calorie restricted diet [4, 5].  That could include fasting until 6pm and consuming your required calories – and carbohydrate – all between 6pm and 8pm.

As long as you’re in a calorie deficient state, fat loss will occur regardless of whether you’re having your rice before or after 6pm.

“Steer clear from bad carbs such as white rice and potatoes”

This one is a little harder to “debunk” as such, given the vast differences between foods commonly referred to as “bad”.  So let’s look at some basic principles and then a couple of examples.

“Bad carbs” are the term often used to describe white starchy foods such as white rice, white bread, and potato, as well as foods high in sugar such as lollies and even fruit.  The fear around this foods can be linked to many things from the standard fear of carbohydrates, to fear of foods with a high glycaemic index (GI) explained here.

GI is basically a value given to the impact of a food on blood glucose as compared to straight glucose.  The common “bad carbs” listed above all have a high GI.  The issue however is that GI does not take into consideration the typical serving size of the food, or the quantity of carbohydrate in it.  Nor does it take into consideration the fact that most people usually don’t eat these foods on their own (apologies if you’re sick for loaves of plain white bread). Glycaemic load takes into consideration the quantity of carbohydrates in typical serving sizes of those foods.

Starchy Foods

An example of the good carbs vs bad carbs debate is sweet potato vs the humble white potato.

Most of this differentiation is based on the vastly different GI of these two foods.  Potato has a GI of around 85 (high) whereas sweet potato has a GI of around 54 (low).  However, both of these starchy vegetables have a relatively similar glycaemic load (cooking variations can alter this), the only differences then being their nutrient density; potatoes being high in vitamin C whilst sweet potatoes being high in vitamin A for example.  Yet the difference in the acceptability in the diet is still vastly different.  Add this information to the fact that potato would usually be consumed with meat and vegetables, further reducing the spike in blood glucose levels.


Fruit is in a different basket all together.  Given the high water and fibre content of most fruits, their impact on blood glucose is relatively low.  I am yet to see a diabetic suffering acute low blood sugar attempt to quickly balance their blood glucose with a punnet of strawberries (which only contains around 10g carbohydrates).

In saying that, some fruit such as bananas do have a higher carbohydrate content and a higher impact on blood sugar.  However, the nutrient density of such fruits must also come into consideration.  Sticking with bananas as an example, you get a nice dose of vitamins C and B6, as well as manganese and potassium.

Refined sugar foods

Sugar dense foods that are low in nutrients (such as lollies) cannot be recommended as such.  However, they can be an occasional part of a healthy balanced diet and labelling them as “bad” does nothing for the guilt that can often get in the way of long term dietary adherence, and subsequently health.

There is no such thing as a bad carb or bad food for that matter.  However limitations on certain foods will be more optimal for both body composition and health.

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  1. Leibel, R.L., et al., Energy intake required to maintain body weight is not affected by wide variation in diet composition. Am J Clin Nutr, 1992. 55(2): p. 350-5.
  2. Longland, T.M., et al., 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. Am J Clin Nutr, 2016. 103(3): p. 738-46.
  3. Sofer, S., et al., Greater weight loss and hormonal changes after 6 months diet with carbohydrates eaten mostly at dinner. Obesity (Silver Spring), 2011. 19(10): p. 2006-14.
  4. Zuo, L., et al., Comparison of High-Protein, Intermittent Fasting Low-Calorie Diet and Heart Healthy Diet for Vascular Health of the Obese. Front Physiol, 2016. 7: p. 350.
  5. Aksungar, F.B., et al., Comparison of Intermittent Fasting Versus Caloric Restriction in Obese Subjects: A Two Year Follow-Up. J Nutr Health Aging, 2017. 21(6): p. 681-685.

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