Carbohydrates are the most common food group consumed during a typical day. They provide energy for all bodily functions such as brain function, heart rate, digestion and other metabolic processes. Carbohydrate intake is considered essential for optimal health and performance. However, there have been some recent reports suggesting that carbohydrate consumption may increase risk factors associated with cardiovascular disease (CVD) and diabetes mellitus (DM).1–3 There are many types of carbohydrates. Some are simple sugars, which include glucose, fructose and sucrose; others are complex carbohydrates, including starches such as rice or potatoes; still others are dietary fibers derived from plants like cellulose or lignin. Dietary fiber reduces the absorption of calories and helps lower blood sugar levels.4 These findings raise questions about whether consuming too much carbohydrate could lead to excess body fat accumulation over time.5
The current recommendation for carbohydrate intake is between 50% and 70% of total daily calorie intake.6 The recommended amount varies depending on age, gender, activity level and other factors.7 Although the American Heart Association recommends no more than 30 g/day of added sugars,8 it does not recommend restricting carbohydrate intake to less than 20%.9 Therefore, it seems reasonable to assume that the majority of individuals consume too much carbohydrate.
In this article, we present the case that carbohydrate consumption is positively associated with weight gain and obesity. We also explore mechanisms by which carbohydrate consumption may cause weight gain. We propose that increased consumption of carbohydrate leads to hormonal changes that promote fat storage, and an elevation in another hormone that reduces the feeling of fullness after eating, leading to excessive food intake. Finally, we provide evidence on whether there is an upper limit of carbohydrate intake for weight management.
Evidence demonstrating that high-carbohydrate diets cause weight gain
Most people in Western society consume more energy (calories) than they need.10 The amount of carbohydrate in one’s diet is strongly associated with weight gain. In general, increased consumption of carbohydrate results in increased energy (calorie) intake. There are several reasons for this.
First, the majority of carbohydrate foods are processed and loaded with added sugars and stripped of dietary fiber. These processed carbohydrates are quickly digested and absorbed, which leads to an elevation in blood sugar and insulin. The elevated insulin levels drive down serum triglycerides and elevate serum free fatty acids. Excess serum free fatty acids drive energy (calorie) intake, and carbohydrate is the macronutrient that can be easily converted to glucose for energy. Second, increased consumption of refined grains, starches and sugars decreases levels of HDL cholesterol.11 HDL transports cholesterol from other tissues such as the intestine back to the liver, where it can be broken down or excreted. Low levels of HDL increase the risk of cardiovascular disease via mechanisms that include the accumulation of excess cholesterol in blood vessel walls.
The great majority of studies establish a positive relationship between carbohydrate intake and weight gain. A 2009 systematic review12 identified 21 intervention trials that had been conducted up to that time. In these trials, the consumption of refined carbohydrates was typically increased by 50% and sustained for one month or longer. These trials enrolled participants who were not on restricted calorie diets, and the increase in weight during the intervention period was an average of 0.9 kg in low-carbohydrate diets and 1.3 kg in high-carbohydrate diets.
Another systematic review13 addresses the impact of consuming additional sugar-sweetened beverages on body weight. This review included only randomized controlled trials that had a follow-up of one year or longer. The conclusion was that increased intake of sugar-sweetened beverages causes weight gain. Sustained intake of sugar-sweetened beverages in excess of 8oz/day for one year or longer resulted in an average weight gain of 1.8kg for adults and 1.3kg for children.
The weight gain caused by consuming excess carbohydrate is not exclusively due to sugars and starches. Some of the weight gain results from an increase in intake of vegetable oils and dairy products, both of which are high in calories and difficult to burn off easily. When The New Glucose Revolution book was first published in 2000, it concluded that replacing foods high in saturated fat with refined carbohydrates resulted in less weight gain.
Sources & references used in this article:
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Effects of 28 days of resistance exercise while consuming commercially available pre- and post-workout supplements, NO-Shotgun® and NO-Synthesize® … by M Spillane, N Schwarz, S Leddy, T Correa… – Nutrition & …, 2011 – Springer
Whey protein supplementation during resistance training augments lean body mass by JS Volek, BM Volk, AL Gómez, LJ Kunces… – … College of Nutrition, 2013 – Taylor & Francis
Post Workout Carbs= Bad by M Di Pasquale – longecity.org
What Is A Proper Pre, During, And Post Workout Nutrition Diet? by WFSYE While – bodybuilding.com
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