Weight Loss on a Low-Carb Diet

What to Expect in the First Month of a Low-Carb Diet

man on scale
Photo: Tom Grill/Getty Images

People are attracted to a low-carb way of eating for a variety of reasons: blood sugar control, to lower blood pressure, and to improve many other health indicators. But there's no doubt about it: most people try cutting carbs in order to lose weight. So, is losing weight different on a low-carb diet? And what can you realistically expect when it comes to weight loss?

Related Resource: What to Do Before You Start Your Low-Carb Diet

How Is the Low-Carb Weight Loss Experience Different?

You may be surprised to hear that on a low-carb diet weight loss mainly happens in the same way as on any other weight loss diet - by creating a calorie deficit (consuming fewer calories than you expend). The difference is that while a low-calorie diet has an externally-imposed calorie limit, a low-carb diet works with your body so that you desire fewer calories. I think of this as changing the demand, rather than the supply, of food. Carbohydrate reduction seems to work on the appetite system in multiple ways, including levels of hormones and other transmitters of information about hunger and satiety in our body. In study after study, people lose approximately the same amount of weight on a low-carb diet as on a low-calorie diet, even though they are not told to limit the amount of food they eat (just the amount of carbohydrate). Because of this, people who respond well to low-carb diets often talk about feeling "normal around food", and not having the compulsions to eat that they usually do, once they adjust to eating a reduced-carbohydrate diet.

The First Week

The first week of a low-carbohydrate diet is a special case. The body has been using primarily glucose for energy and must switch to using primarily fat. This means that it's the least comfortable time (Here are some tips to help you over that hurdle), but it also means that a few pounds will be lost that are not fat, but water.

This is not because of being bloated, but because the glucose which is stored for easy use in our liver is in a molecule called glycogen, which is bound up with a lot of water. When we use the glucose, our bodies get rid of the extra water. In the normal course of a regular diet with stable weight, the amount of glycogen fluctuates only a little, but during weight loss, and especially weight loss from low-carb diets, the amount of glycogen is reduced, and with it, the water.

Tides of Water Weight Going Out...and then Back In

This reduction in glycogen accounts for the quick drop of a few pounds that first week. While everyone on a weight loss diet loses some "water weight" this way at first, it is more pronounced on a low-carb diet. This because all carbohydrate breaks down into simple sugars like glucose in the body, so the supply of glycogen is dramatically reduced.

The loss of water weight in the first week has led some critics of low-carb diets to declare that all the weight lost on a low-carb diet is water. This, of course, is ridiculous. As one low-carber quipped in response to this claim, "Well, I guess that's 50 pounds of water I didn't need!"

One of the interesting, and sometimes discouraging, things about this water is that once gone, it doesn't all stay gone.

Returning to eating a higher level of carbohydrate will definitely increase the amount of glycogen stores, causing overnight weight gains (but not, of course, fat gains). But even if you don't go back to eating a lot more carbohydrate, glycogen stores gradually build back up to somewhere around 60% of what they were (the glucose mainly coming from gluconeogenesis from protein). This is not at all a bad thing -- our bodies need to maintain a certain level of blood glucose, and having a reserve is an important "slush fund". But these changes can really do a number on scale-watchers who are anxiously tracking those lost pounds.

Even when you are losing fat, those tides of water flowing in and our of your body for this and other reasons create what looks like stalls in your weight loss. The trick is not to get too tied to the scale during this time.

The Second Week

I think of the second week as a week of consolidation after the roller coaster ride of the first week. You should start feeling more stable, and your appetite should be adjusting. This is where the real fat loss will start in most people who respond well to low-carb diets. Some bodies do take a little longer to adjust, however. It's not all that uncommon for me to hear from people for whom it took a few weeks for obvious weight loss to begin.

The Next Few Weeks

Sometime in the second half of the first month, your body will probably settle into a pattern of weight loss. The rate at which you lose depends on many factors, the most prominent of which is how overweight you are to start out with. People with less to lose will lose much more slowly than those with a lot of extra fat. Also, men tend to lose more rapidly than women, probably partly because of size, but hormonal differences, muscle mass, and other factors may also play a role. There is also a great deal of genetic variation. Studies with identical twins on identical weight loss diets generally show a very similar pattern of weight loss within the twin pairs, while between twin pairs there can be extremely large differences.

How and When to Weigh Yourself

Generally, once the first couple of weeks is over, people will lose between half a pound and 2 pounds per week. This rate is considered safe. The usual advice is to weigh yourself once a week because day-to-day weight fluctuations due to fluid, fiber consumed, and other factors can be discouraging. Also, women who are having menstrual cycles sometimes decide not to weigh in the second half of their cycles, especially if they tend to retain water at this time.

It's important to choose a consistent time of day to weigh yourself. Most of the time people choose to weigh first thing in that morning, before beginning to eat and drink, because this is the best basis for comparison. If you weigh at another time of day, there will be even more fluctuations.

If you've made it through the first month, congratulations!! You've made it through the toughest part of making a life change.


Browning JD, Weis B, Davis J, Satapati S, Merritt M, Malloy CR, Burgess SC. "Alterations in hepatic glucose and energy metabolism as a result of calorie and carbohydrate restriction." Hepatology 48(5):1487-1496. 2008.

Gardner, Christopher, Alexandre Kiazand, Sofiya Alhassan, et al. "Comparison of the Atkins, Zone, Ornish, and LEARN Diets for Change in Weight and Related Risk Factors Among Overweight Premenopausal Women." Journal of the American Medical Association 297-9. 2007.

Shai, Iris, et al. "Weight Loss with a Low-Carbohydrate, Mediterranean, or Low-Fat Diet." The New England Journal of Medicine 359:229-241. July 17, 2008

Continue Reading