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Dear Mark: Should I Increase Carb Intake for Weight Loss?

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 [7], stops, or requires new input to continue like it was is ultimately okay, because we are an adaptive species. We can change things up [8], shift stuff around. Physiological processes (among which weight loss and metabolism can certainly be counted) are never linear [9] – 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 [10] and carb refeeds [11] 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 [12]. 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 [13], perhaps independently of the increase in insulin [14], 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 [15] in order to protect against further weight loss, and that supplementary leptin kickstarts weight loss all over again.

Ultimately, then, leptin is how the body senses both incoming and stored energy. It goes up in response to food eaten, as well as food stored. And since day-to-day survival of an organism is largely about energy availability, the presence or absence of leptin can make life pretty awesome or pretty awful. This doesn’t just impact weight loss or gain; it impacts your enjoyment of life. Low leptin? You might not feel like taking that walk with your friend. You probably won’t want to work out. Your libido might suffer. You might not feel like doing much of anything except sit around.

Can you see why lagging leptin might be an issue in stalled weight loss during a diet? You’re dropping calories (an indicator of reduced energy availability), dropping body fat (an indicator of reduced energy availability), and, especially if you’re low-carb, you’re dropping insulin and carbs (an indicator of reduced energy availability). All these things tell the body to make less leptin, and less leptin means higher appetite (so you eat more) and lower energy expenditure (so you burn less fat and don’t feel like doing much of anything).

How Should You Do It?

As I mentioned in the refeed post, keep the fat content of your meals down when doing a carb feed – about 50 grams for the day. Why? For one, fat doesn’t have as much an effect on leptin as carbs or protein do, and two, since triglycerides have been shown to prevent leptin from crossing the blood-brain barrier [16] (into the brain where leptin does its work), the increased postprandial triglycerides (which are a normal, temporary, physiological consequence of eating fat and different from elevated fasting triglycerides) may reduce the effectiveness of leptin.

The greater you normally restrict carbs, the more you eat on your refeed. If you’re hanging out in the 100-150 gram range, you probably won’t need much – if any – of a boost in carbs. If you’re below 100 grams, I’d do 250 grams or so. If very low carb (below 50 grams), shoot for 300-350.

Do your refeed on a training day. Lift/sprint/run/hike/play big and, then, eat big. Your insulin sensitivity [17] and leptin sensitivity will be high [18], your glycogen will be depleted, and you will basically be set up to store/burn the carbs and muscle energy rather than store it as fat. Leptin will increase regardless if you train or not, but doing it on a training day will mitigate any metabolic fallout.

Don’t use this as an excuse for stuffing your face with garbage. I mean, I suppose you could truly turn it into a cheat day and eat a couple pizzas, a gallon of ice cream, and a platter of crispy oxidized soybean oil-infused whatevers, but you’ll have better results with potatoes [19] and yams (or even rice [20]) and animals.

Who Shouldn’t Do It?

A big carb feeding isn’t right for everyone. I would say that for the severely overweight-to-obese, you should not be messing around with carb feeds. It’s not that they’ll wreak irreparable amounts of damage on your metabolism or anything; they just won’t be very helpful. See, the obese tend to be insulin-resistant (PDF [21]). They have tons of leptin in circulation, far more than lean individuals, but it cannot do its intended job [22]. Instead of telling the muscles to burn more fat for energy and telling the brain to quell the appetite, leptin’s message in the obese is muffled, stifled, hamstrung. It can’t get through. Lack of leptin is not the problem, as the considerable amounts of adipose tissue are doing a fine enough job manufacturing the stuff. Sensitivity to leptin in the brain and periphery is the problem. Thus, adding more leptin to the bunch via dietary manipulation won’t help, and it may even compound the problem. Improving leptin sensitivity is the real issue here, and a lowish-carb Primal eating [10] and general lifestyle plan [23] (with adequate sleep [24], smart training [25], and plenty of stress mitigation [26]) is the best way to do that.

Who Should Do It?

Leptin is most effective in the lean, moderately lean, and somewhat chubby (yes, those are absolutely technical terms). Men with six-packs, four-packs, two-packs, and men and women with a light layer of subcutaneous blubber covering everything up tend (a la those hunter-gatherers who aren’t exactly “ripped,” but definitely not unhealthy) to be essentially leptin-sensitive. In these individuals, leptin acutely boosts skeletal muscle fatty acid oxidation [27].

Those with “stubborn” body fat, those on an extended stall, or the otherwise lean who can’t quite seem to get the last dozen pounds to disappear are prime candidates for a big refeed. They’re not so overweight that leptin resistance is likely, so they’ll benefit from a general increase in leptin. They’re fairly lean, so circulating leptin is lower.

Anyone who’s “feeling off” from low-carb Primal, despite their best efforts. Say you’ve given the low-carb flu [28] a chance to pass over, you’ve addressed your sleep [29] and stress [30], you’re not trying to train like a pro athlete, and you’re still feeling run down and unable to lose weight? Throw in a big carb feed.

What about you guys? Have you experimented with carb refeeding, and if so, how did it impact your weight loss efforts?

Thanks for reading!