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Boosted by the popularity of the Atkins diet in the late 90s and early 2000s, low carb diets have long been glorified in the diet industry. As a result, carbs have inherited a bad rap as leading to inevitable weight gain if consumed. Instructions to ‘cut back on carbs’, ‘eliminate bread, pasta and wholegrains’ and ‘avoiding the whites’ has become the ‘go-to-advice’ for those bypassing education to get to the crux of how to lose weight. Let’s use science to bust some of the ‘carbs make you fat’ myths allowing you to be carb fear-free and bring back #CarbsAfterDark too!

Our client Sage who achieved fat loss results and changed her body composition under our coaching. This is has been achieved through a non-restrictive diet incorporating roughly 40% carbohydrates!

Myth Busting...

1. Carbs spike your insulin

Every time we eat carbs we’re told our insulin level spikes which is insinuates that our body - in response - stores everything as fat. So as a preventative and to keep insulin levels as low as possible, people use this as justification to cut carbs. Insulin is a hormone produced by the pancreas and its role is extremely important. When you eat food, the nutrients it contains make their way into your bloodstream along with insulin. Insulin tells cells to ‘open up’ to receive the nutrients and thus causes them to be absorbed into muscle and fat tissues[1]. Research suggests that, while it does increase with the consumption of carbs, the amount of insulin your body produces in response to eating food (‘insulin response’ as it’s referred to) doesn’t affect the amount of fat stored or gained[2]. Fat storage is essentially just a part of the consumption and expenditure process.

After eating, the body goes into ‘fat storage mode’. This is essential as when glucose levels rise far above what is needed to maintain life after consuming food, instead of “throwing away” or burning off all excess energy, a portion is stored as body fat for later use. Once the body has finished absorbing the glucose and other nutrients from the food (amino acids and fatty acids), it then enters the “postabsorptive” state (“after absorption”), wherein it must turn to its fat stores for energy. This “fasted” state is when the body is in “fat burning mode.” So you’re constantly flipping between ‘fed’ and ‘fasted’ states every day, storing fat from food you eat, and then burning it once there’s nothing left to use from the meals[3]. 

The above image demonstrates the periods when your body has excess energy due to having eaten food (fat storage mode), as well as the periods where the body turns to the fat stores for fuel (fat-burning mode). 

This is the fundamental mechanism underlying fat storage and fat loss and it takes precedence over anything related to insulin or any other hormones in the body. Simply put, you can’t gain fat unless you feed your body more energy than it burns, and you can’t lose fat unless you’re consuming less energy than burning. Research supports that reduced-calorie diets result in clinically meaningful weight loss regardless of which macronutrients they emphasise[4], dubbing insulin levels and the amount of carbs you eat irrelevant.

2. Carbs at night make you fat

The broscience assumption about carbs at night is that since you will be going to sleep soon, your metabolism will slow down and those carbohydrates will have a greater chance at being stored as fat compared to if they were consumed earlier in the day where they would have a greater probability of being burned. This assumption, while it seems to make sense, has been proven false by a number of scientific studies and principles. As noted by Layne Norton[5] there are studies that have been conducted showing energy expenditure decreases during the first half of the night by approximately 35%[6]. However this research failed to show that during the latter half of sleep energy expenditure significantly increased in association with factors such as REM[7] (rapid eye movement). During sleep, there are rises and falls in your sleeping metabolic rate; Layne Norton states after examination of a number of studies it does not appear that the average overall energy expenditure during sleep differs to the resting metabolic rate during the day[8][9][10] .

If you train, then it can increase your sleeping metabolic rate as well as your fat utilisation during sleep. So unless you’re obese - in which obese individuals have demonstrated to have had a lower metabolic rate to their resting metabolic rate[11] - then not only does your metabolism not slow during sleep but it’s actually been shown to increase[12].

As mentioned in point 1, the fat loss principle of energy in vs energy out surpasses any concerns regarding carbs at night or meal timing, so don’t overcomplicate it or restrict to achieve your fat loss goals. A recent study[13] conducted using two groups of people consuming the same amount of protein, carbs and fats on a restricted-calorie diet with a different distribution of carb intake over the day showed the following:

  • Those who consumed the majority of their carbs at night after 6 months lost more weight and body fat

  • Had better satiety

  • Had less hunger 

3. Carbs are not essential

There are a number of issues with not eating carbs hence justifying their necessity in your diet. For the most part, anyone with success due to a low carb diet has achieved this through essentially cutting an entire macronutrient from their intake therefore decreasing overall calories. So, it's less attributed to the fact that carbs were cut but rather that fewer calories are being consumed than expended. Carb reduction comes at a cost though, both short and long term. Carb consumption is essential particularly amongst those active individuals and those who exercise. Drastic reduction can lead to:

  • Decreased thyroid output- T3 goes down, reverse T3 goes up, further blocking T3[14]

  • Increased cortisol output -  Cortisol is a hormone produced by the adrenal glands in response to stress, such as the physical stress of exercise, studies have shown that cortisol increases particularly in those who train if carb restriction occurs[15]

  • Decreased testosterone - Lowered testosterone can affect overall body composition decreasing muscle mass and potential to gain muscle. Lowered testosterone can impact anabolic effects on muscle and also decrease basal metabolic rate (BMR). It's also important for overall health and well-being[16]

  • Impaired mood and cognitive function - Low carbohydrate diets can affect overall energy and mood increasing emotion of sadness and anxiety as well as affecting overall mood and memory function[17]

  • Muscle catabolism - Low carb diets can lead to muscle breakdown, due to severely lowered insulin levels[18].

  • Hormonal deficiencies - Women can face hypothalamic amenorrhea due to not eating enough carbohydrates, which is where hormones are disrupted and periods can stop because of the HPA’s response to perceived starvation and stress. You end up with low levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), estrogen, progesterone, and testosterone[19]

  • Suppressed immune function

In summary, carbs are essential and without them your metabolism may slow, stress hormones increase and muscle building capacity decreases. So in turn this can have you feeling spaced-out, fatigued, sluggish, moody and even ill.

white and brown sugar

4. Sugar is toxic and makes you fat

Some people make distinctions between ‘natural’ sugars such as those found in fruit and raw maple syrup and ‘processed’ sugars such as table sugar and high-fructose corn syrup. (And often these people will say the natural sugars are ‘okay’ but the processed sugars are evil).

All forms of carbohydrate we eat are either metabolised into glucose or are left undigested, serving as dietary fibre. Our body can’t distinguish between the natural sugar found in fruit, honey or milk, and the processed sugar found in a Snickers bar. They’re all digested in the same way: they’re broken down into monosaccharides, which are then turned into glucose, which is then shipped off to the brain, muscles, and organs for use[20]. 

Sugar has been demonised in the media but much of the research suggests that sugar isn’t the catalyst, rather the problem is that sugary foods are typically low in fibre. This is why refined sugary foods that have low fibre tend to lead to problems when over consumed, but consumption of fruit does not seem to have the same effect, because fruit has fibre [21].

Many studies have compared groups eating a diet with the same macronutrient composition (same ratio of protein, fats and carbs) with only differing carb sources. The groups eating lots of sugar lost the equivalent body fat without losing more muscle mass as opposed to the groups consuming little or no sugar[22][23]. In studies where complex carbs like whole-wheat bread were replaced with sugar but the total caloric intake was kept constant, no body composition changes took place[24]. So as long as you track your macros, having sugar in your diet is in itself not bad for your physique. And it gets even better.

So sugar is merely misconceived, ‘it can’ rather than ‘it does’. For example, sugar scores very low on the satiety index as it doesn’t fill you up relative to how much energy you consume. So, if you add sugar to a meal or have a high sugar meal, you’re likely to clean the plate and be wanting more. Sweetness is tastier, and during consumption oblivion to the calories is common as your stomach doesn’t feel full, disproportionate to the energy consumed. Adding sugar to your meals (this is fine if factored into your daily consumption) may increase your energy intake, since your body follows the laws of physics, specifically the laws of thermodynamics, what happens to your weight depends on your body’s energy balance. You gain weight in an energy surplus because energy will be stored. You lose weight in an energy deficit, because your body will have to oxidise AKA burn body tissue to get enough energy[25]. What causes weight gain is feeding your body more energy than it needs every day, regardless of what foods are providing the excess energy.

So in summary, why are carbs good?

  • Satiety: keeping you fuller for longer- eat a bunch of fibrous carbohydrates and you’ll feel very full for quite some time and less likely to overeat 

  • Fuel for your workouts: through avoiding a reduction in glycogen stores[26] which can compromise your performance in the gym – without carbs you can expect a dramatic reduction in both muscle endurance and strength. This can limit the amount of progressive overload you can subject your muscles to in those workouts (less overload = less growth over time)[27]

  • Energy: Carbohydrates are the body’s main source of energy, without them you’ll feel tired and sluggish

  • Muscle preservation and growth: When dieting, you want to preserve as much muscle as possible as the more muscle you have, the higher your metabolic rate is. When muscle glycogen levels are low, post-workout signalling related to muscle growth is impaired. This is especially unwanted when you’re dieting for weight loss because a calorie restriction alone already impairs your body’s ability to synthesise proteins[28]

  • Strength and recovery: Studies have shown low carb diets cause lowered strength, slower recovery, and lower levels of protein synthesis[29]

  • Healthy immune system: A healthy immune system benefits from a diet high in omega 3 fats, fresh fruit and vegetables, nuts and whole grains, most of which come from carbohydrate sources

  • Increasing or maintaining BMR: Maintaining lean muscle mass (and testosterone levels) through carb consumption - avoiding catabolism (muscle breakdown due to lack of energy) helps increase your daily energy expenditure

  • Reducing cortisol: Cortisol acts to increase glucose availability by mobilising amino acids from muscle (gluconeogenesis), essentially "stealing" muscle to fuel high-intensity exercise

  • Avoiding testosterone reduction: Your testosterone-to-cortisol ratio may well determine whether you're in an anabolic or catabolic state, as well as this low testosterone can reduce BMR and affect body composition

  • Palatable: Carbs are delicious!

  • Fibre: Most carbohydrate sources (mainly complex carbs) are fibrous. 

  • Balance: Excluding an entire macronutrient from your diet is unbalanced and restrictive, in which case the deprivation can lead to binging and unsustainability 

 pastries and coffee

How many carbs should you have?

The minimal recommended carbohydrate intake is 130 grams per day for the general population. The amount of carbohydrate that should be consumed depends on body size and activity levels: bigger and/or more active people need more while smaller and more sedentary people require less. Intake is also dependent on dietary fat and protein intake.

The minimal recommended intake for fibre is 25 grams per day. The optimal amount is around 35 grams/day for women and 48 grams/day for men. Fibre comes in different forms (soluble/insoluble) and is important for satiety, blood fat levels[30], colon cancer, motility and gut health[31][32]. Fibre is found in vegetables, legumes, fruits, nuts, seeds, and whole grains[33].

Should you ever cut carbs?

The only time when you could actually benefit from low-carb diets, is if you have some serious issues with insulin-resistance, or leptin-resistance (don’t self diagnose these issues yourself!), or if you’re prepping up for a bodybuilding show and need to drop water weight. If you don’t fit in any of these categories, then there’s really no need to omit from carbohydrates.

In conclusion, carbs are our friends and science agrees. Enjoy them!


1. 2.
6. Katayose Y, Tasaki M, Ogata H, Nakata Y, Tokuyama K, Satoh M. Metabolic rate and fuel utilization during sleep assessed by whole-body indirect calorimetry. Metabolism. 2009 Jul;58(7):920-6.
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