Do carbs make you gain weight?

Why do carbs get a bad rap?

Some are convinced that eating carbs piles on the pounds. They may have followed a no-carb diet rigidly for a week or two, shed 4 or 5lbs and then given in to the pleasure of a slice of toast with their boiled egg at breakfast, had some pasta with a tuna salad lunch and added a few potatoes to the evening meal of chicken and veg.  

​... And when they step up onto the scales the following day ... horror of horrors, as they see a gain of a couple of pounds in just 24 hours, and wonder, “How can this be?” The blame may fall on the bread, pasta and potato, and they wrongly conclude that carbs make you gain weight.

The different types of carbs

There are two main types of carb, one is the starchy carbohydrate found in potato, rice, yam, green banana, bread, pasta couscous and the like.  And the other type of carbohydrate are the sugars found in fruit, honey and the huge amount of processed foods that have sugar added to them – this makes a product taste good, look good and feel good as we chomp our way through whatever it is.
 
Fermentable carbs feed gut-friendly bacteria

And then there are types of carbohydrate that we don’t have the ‘tools’ to breakdown and these are fibre and short-chain carbohydrate, such as in onion, garlic, pulses, wheat, cabbage and many other plant foods.  Our gut-friendly bacteria do have the ‘tools’ to breakdown those types of carbohydrate, and most of that fermentation takes place in the colon.  
 
This is a good thing, despite it being a cause of excessive gas in some people ...

The diversity of our microbial friends may play a part in weight management – research shows that weight gain is lower when we have lots of the different types of bacteria in our colon. And there are fewer different types of bacteria in our gut when our fibre intake is low.

Glucose carb is our primary source of energy 

Back to the question, when people talk about carbs causing weight gain, they are usually referring to starch and sugar carbs. Both types are a source of the glucose sugar used for energy by muscle, brain and every other organ in our body.  

Glucose fuel is kept in storage (as glycogen) in our muscle and liver.  Eat or drink more carbohydrate than can be stored in that ‘tank’ and the excess will be converted to fat and stored in the places where you’d rather it wasn’t!
 
A low-carb diet produces ketones

At the other end of excess carb consumption there is low-carb eating and drinking.  A very low intake of carbohydrate causes the body to produce ketones (derived from fat), and you may have heard the term ‘ketogenic diet’. This very restricted diet is actually proven to help in the management of epilepsy, but we’re talking about weight management here, rather treatment of epilepsy, so let’s stay with this with regard to a ketogenic diet.
 
A low-carb diet or keto diet will, of course, bring about weight loss when calories consumed are less than calories used by the body’s organs and muscle that move us around.  But carbs themselves don’t make us gain weight, any more so than does fat or protein, unless we eat any of those nutrients to excess.  

It simply comes down to energy balance: our weight is stable when we consume the same number of calories as we expend. Spend a few days eating more calories (doesn’t matter whether from carbs, fat or protein) than spent and the scales will soon tell you what you’d rather not know.

Yes, you can lose 7lb in 7 days on a keto diet, but ...
 
People will say, “I lost 7lb in a week on a low-carb diet”.  Sure, that’s possible, because at least 4lb of that weight loss will be water (not fat) – water is lost following depletion of muscle and liver glycogen stores.  On average, we store around 1lb of glycogen, which is stored with 3lb of water – lose that 1lb of glycogen and you lose that 3lb of water.  Those same people won’t lose another 7lb over the next seven days, because the glycogen stores ran dry the previous week.  
 
But, despite big weight loss in that first week, will they stick to the low-carb diet?

How many of us could refrain from eating bread, pasta, potato, cake, biscuit, chips and other sources of delicious carbs ever again? It wouldn't be easy that's for sure - it's much better to start off as we mean to go on  ...
 
Moderation is the key to sticking to a diet. Extreme restriction is no fun, but there’s a happy middle ground between denying yourself carbs and consuming to excess.  The take-home message: eat carbs, not too much, control your weight.
 
Have you ever tried a low-carb or keto diet? Did it work for you? How long did you do it for?

Tony Hirving
Dietitian