How many times have you heard that you should eat NO CARBS after 6 PM? When it comes to fat loss, is this “carb curfew” a good, evidence-based rule of thumb? Or, is it simply more diet dogma and nutritional nonsense?

How Does the Carb Curfew Work?

I’d like to think that rules like “no carbs after 6 PM,” often backed by celebrity endorsement, have some credible scientific basis. And to some degree, the “carb curfew” does have some merit. For instance, research on circadian biology shows us that carb tolerance and insulin sensitivity are greatest in the morning. They then decline over the course of the rest of the day. In other words, biologically speaking, our bodies seem primed to use carbs earlier in the day with varying degrees of resistance setting in through the day.

That said, this line of thinking suggests carbs eaten at nighttime—regardless of total daily caloric intake—are more likely to be stored as fat (compared to, say, when the same foods are eaten at breakfast). As compelling as that argument sounds, it ignores the basic tenet of energy balance. To lose weight, you’ve got to eat fewer calories than you burn on a regular, consistent basis. That is, you need to create a negative energy balance. While there’s certainly more to the equation than “calories in vs. calories out,” we can’t turn a blind eye to this fundamental principle guiding weight management.

Further, recent research clearly refutes the carbohydrate-insulin theory of obesity, which states carbohydrates are particularly fattening because they elevate the hormone insulin. This, in turn, increases fat storage and blunts fat burning. As we’ve talked about before, diets with varying compositions (low-fat vs. low-carb) can both be effective for weight management. At the end of the day, how much seems to be the most crucial factor. Along those lines, food choices and portion sizes seem to be the most important variables.

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Of course, when someone suggests you eat no carbs after 6 PM, s/he is probably not talking about healthfully prepared “smart carbs.” Carbs like veggies, fruits, legumes, and minimally processed whole grains. At least they shouldn’t be. Rather, the effectiveness of the carb curfew is likely to hinge on two premises:

1. You’ll restrict your consumption of high-calorie, carb-containing entrees, processed foods, and junk (such as pasta dishes, fried foods, pizza, chips, candy, ice cream, etc.)
2. More importantly, you’re likely to restrict your overall caloric intake, which is still the most important and fundamental principle for meaningful fat loss.

No Carbs After 6 PM Refuted?

Admittedly, there isn’t much research that puts the “no carbs after 6 PM” advice to the test. In and of itself, that gives us an indication that the scientific community thinks it’s nutritional nonsense. However, one study published in the journal Obesity comes to mind. What’s interesting is that it offers evidence counter to the ol’ carb curfew.

In the study, researchers assigned 78 Israeli police officers to one of two reduced-calorie diets for six months. Both groups consumed the same number of meals and foods throughout the day. One group followed a “normal” diet with calories and carbohydrates spread out through the day. The other group was assigned to an “experimental” diet in which they consumed a larger percentage of their calories (and carbohydrates) in the evening.

Both groups lost weight, body fat, and inches from their waistlines. But here’s the kicker: the “experimental” group, which ate most of their carbs in the evening (presumably after 6 PM), experienced significantly greater improvements in all three areas. What was particularly intriguing was that this strategy of eating more carbs later in the day led to improved profiles of hormones related to hunger, satiety, and metabolism (e.g., leptin, ghrelin, adiponectin).

This shift in hunger hormones resulted in less hunger throughout the day. So, it’s feasible to conclude that the participants who violated the no carbs after 6 PM rule were more compliant with their diets compared to folks who were asked to abide by the carb curfew.

In addition to helping some folks stick to their plan, eating carbs—“smart carbs,” of course—later in the day may offer a couple of other benefits. First, eating some carbs may help reduce levels of the stress hormone cortisol (since insulin counteracts cortisol). This is important because an excess of cortisol or out of rhythm hormones can negatively impact health, body composition, sleep, and more. Also, carbs promote the release of the “feel-good” molecule serotonin. This promotes satiety, feelings of wellbeing, and a restful night’s sleep.

No Carbs After 6 PM ≠ Magic

This leads us back to one of the initial points made. Fat loss still comes back to energy balance. If setting a carb curfew for yourself helps you limit food intake, then go for it. However, if it leads you to overeat—no matter what time of day—and deviate from your plan (i.e., non-compliance), then you’re not going to get the results you expect.

Can restricting yourself to no carbs after 6 PM help you lose weight? Sure, but it’s not magic, and for those interested, it’s not a scientifically sound recommendation. If it “works,” it’s because it helps people restrict calories, especially intake of high-calorie processed foods.

If you like things in black and white, then a guideline like no carbs after 6 PM could be useful for you. However, if you like science, you’d probably consider this nutritional nonsense and diet dogma—and I wouldn’t blame you. However, we have to remember the ol’ cliché “different strokes for different folks.”

Regardless of why something like the carb curfew “works,” we have to consider it a tool in the toolbox if it helps someone improve diet quality (e.g., food choices and portion sizes).

Lastly, we shouldn’t throw the baby out with the bath water per se just because “no carbs after 6 PM” may be founded on celebrity endorsement instead of solid science. Specifically, there’s compelling and mounting evidence that eating at the right time and even restricting the amount of time you eat may be tremendously important for weight management and overall health.

Along these lines, an appreciable amount of research (granted, much of it is observational nature) suggests eating a larger proportion of calories (especially if you eat carbs) earlier in the day (as opposed to “breakfast skipping”) may be advantageous for overall health, glycemic control, insulin sensitivity, and weight management. This seems to relate back to circadian rhythms, as meal timing has been shown to have a substantial effect on the body’s internal clocks.

The take-home point is that you don’t need to restrict your carbs after 6 PM to lose fat. In fact, many people find that including “smart carbs” can help them stick with their diet plan, reduce cravings, increase feelings of satisfaction, improve quality of sleep, and even promote healthy cortisol rhythms.