Should You Increase Carb Intake To Lose Weight?

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Sometimes, weight loss slows. Sometimes, what worked amazingly well before, stops working quite the same. Although this can be scary, frustrating, annoying, or all of the above when progress slows, stops, or requires new input to continue like it was is ultimately okay, because we are an adaptive species. We can change things up, shift stuff around. Physiological processes (among which weight loss and metabolism can certainly be counted) are never linear — that’s partly what makes all this stuff so endlessly engaging.

Today, I revisit a strategy for overcoming these lulls in weight loss induced by low carb: carb (re)feeds. They seem counterintuitive, sort of, especially if you’ve had success restricting carbs, but hold you opinions until you read on. I think you’ll find it enlightening.

Dear Mark: Your blog is a treasure trove of valuable information. Thank you for keeping this resource available to us!

This is a question that I think many of your readers would appreciate seeing addressed in a post. [Background: I've been studying (and trying, periodically) various low carb regimens for many years, with varying degrees of success. I'm looking to metabolize off about 30-40 pounds of excess fat, build lean muscle and optimize my health and fitness.]

My question is, what do you think of the increasingly common recommendation (from various diet and fitness gurus) to “spike” calories and carbs one day per week, in order to keep the body from down-regulating certain mechanisms too much due to continued low carbohydrate intake? The theory is that a once-per-week carb/calorie spike gives the metabolism a boost, and keeps weight loss going at a better rate than simply sticking to the low carb regimen seven days per week.

I’m wondering if this recommendation for one “free day” per week is helpful or harmful to the objective of significantly reducing excess body fat over a period of a few months, and staying lean for life. I don’t mean a “be a fool and eat garbage” day, but an honest “spike the carbs and calories with healthy foods” day. What do you think: Would this be a weight loss booster overall, or just a setback on the road to burning excess fat and getting to an optimally lean body composition?

Thanks, Mark! I (and I’m sure your other readers) will value your opinion on this.


I’m happy to help. Thanks for the kind words.

Short answer: Yes, I think there is something to the lowish-carber’s occasional carb and calorie fest. Its relevance to a given individual depends on that person’s metabolic situation, of course, but I wouldn’t dismiss it out of hand. Check out my previous posts on leptin and carb refeeds and weight loss to get an idea.

Longer answer: If you’re eating low-carb and low-calorie (which low-carb tends to promote on account of its inherent satiety) and the weight has stopped dropping, you may be low in leptin. Why does leptin matter, and what do calories and carbs have to do with it?

Leptin is a hormone that fulfills two primary roles, as far as metabolism and weight loss go — it increases (or lowers) energy expenditure, depending on perceived energy availability, and it inhibits appetite. Both actions actually happen in the brain, but it’s leptin that gives the brain the message. If perceived energy availability is “low,” energy expenditure drops and appetite increases. If perceived energy availability is “high,” energy expenditure increases and appetite drops. That’s a quick and dirty (and incomplete) overview, but it serves our purposes for today’s discussion.

How does the body “perceive” energy availability?

Body fat is, quite literally, stored energy. It’s also an endocrine organ that secretes leptin, the amount of which in circulation is directly proportional to the amount of adipose tissue on your body. So, the leaner you get, the less body fat (and less stored energy) you have available to drive leptin secretion. Even if you’re not as lean as you’d prefer to be, your lower body fat levels are low enough that the brain isn’t getting the “high energy availability” message from leptin.

Insulin is another indicator of energy availability. Sure enough, insulin increases leptin secretion in fat cells. As far as the body’s concerned, if insulin is present in significant amounts, food has just been eaten, which means food is probably available in the environment. If food is readily available, the body doesn’t need to cram as much food in, nor does it have to conserve energy. It can do things that aren’t essential to immediate survival, like play a game, have sex, go explore, or work out, because there’s plenty of energy available. Leptin goes up, reducing appetite and increasing expenditure. Problems arise with leptin resistance, of course, when your insulin is constantly elevated, but I’ll get to that later.

Carbohydrate content of the diet, perhaps independently of the increase in insulin, also affects leptin levels. Protein also increases leptin, and fat seems not to, but carbohydrates have the largest effect.

Overall calorie content of the diet is an indicator of energy availability. Studies show that calorie restriction causes the body to lower serum leptin levels in order to protect against further weight loss, and that supplementary leptin kickstarts weight loss all over again.

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