IN the mid-1990s, people were starting to talk about carb-restriction as the answer to dieters’ prayers — the South Beach Diet, the Atkins’ Diet, and others, evangelised the benefits of replacing potatoes, bread, pasta and rice with red meats and fatty foods that were traditionally no-nos.
We were told the results would be dramatic, and in many cases they were. A new industry emerged, its brave new ‘low-carb’ philosophy challenging the long-held dietary dogma that fats were the ‘baddies’ and the cause of dramatic increases in obesity.
But could avoiding carbs be the solution to all our weighty woes? To answer, we have to understand more about how carbs work in the body, and how our metabolism changes when we cut them out.
Carbohydrate is a relatively scarce, and extremely valuable source of energy in the body, because certain tissues and organs, most notably the brain, don’t like to burn any fuel other than carbohydrate to get their energy. And if we can’t fuel the brain, it will begin to shut down.
That’s a drastic circumstance to let arise for want of carbohydrate, so the body has two choices: The first is to eat carbohydrate, in the form of starch or sugar, in which case the shortage will be resolved and brain function will return to normal.
The second option is to seek an alternative fuel source for the brain, and for other ‘fussy’ tissues and organs. This is an option that’s rarely deployed, except in famine conditions when there’s no food available and carbohydrate intake isn’t possible.
In this desperate situation, the body calls upon its emergency energy machinery to break down fat to ketones, the only other viable brain fuel. This process is called ‘ketosis’ or ‘ketogenesis’, and it’s this metabolic shift we’re artificially initiating when we deprive the body of carbohydrate on a low-carb diet.
The problem is that it works, meaning that those who want weight loss at any cost will readily sign up, as long as they get results.
There are two difficulties.
Firstly, there’ll be an excessive intake of protein and fat in any diet that restricts carbohydrate — excess protein puts the liver and kidneys under pressure, while the risk of high cholesterol, heart disease, and certain cancers rises as intake of saturated fat, and its associated foods, increases in the diet. The second difficulty is that certain critical nutrients, including vitamins B1, folate and vitamin C, are lost from the diet by avoiding fruit, vegetables and starchy cereals.
Just because carbohydrate restriction permits weight loss, it doesn’t automatically follow that having a normal carbohydrate intake causes weight gain. The latter has been the assumption incorrectly put forth by many advocates of the ‘low- carb’ mantra.
High carbohydrate diets are almost invariably associated with better weight-control than high-fat diets. However, this needs to be qualified by two important provisos:
1. The carbohydrate needs to be derived from starchy, preferably high-fibre sources, and not from refined sugar found in sweet foods, and especially not from sugar-sweetened drinks.
2. For carbohydrate not to contribute to weight gain, you must be sufficiently active. In other words, you need to move around to burn-off this carbohydrate-based energy.
This is a critical point — after all, starchy foods are what our bodies are designed to run on, they’ve been part of our ancestral diets for millennia.
Starchy foods have been linked to weight gain in recent decades due to the dramatic decline in our activity levels as sedentary, labour-saving technology and plain old laziness have gripped the globe.
*Dr Daniel McCartney, lecturer in human nutrition and dietetics at DIT
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