From Atkins to Keto: Here's How Low Carb Diets Really Work

Has the actor Rob Lowe recently let you in on his “little chocolate-peanut butter secret?” If so, you were likely watching an ad for the Atkins Diet, a meal plan company that promotes weight loss through a "low carb” diet. 

Meal plans that cut back how many carbohydrates you eat have promised slimmer waists for decades. The science behind this claim has drawn on just as long, and won’t be stopping soon. “The research will be ongoing forever,” says Jessica Alvarez, a registered dietician who studies metabolism and Type II diabetes at the Emory University School of Medicine. Though the studies are hard to do, it seems the dietary choice can lead to (at least temporary) weight loss. How exactly that happens, however, remains unclear.

The original biological premise behind a low-carb diet was fairly straightforward. Carbohydrates trigger the release of insulin, a hormone that prompts tissues to absorb sugars and produce fat. At the same time, too many of these nutrients will slow your metabolism while growing your appetite.

In theory, if you eat fewer carbs, less insulin will pump through your body — triggering less fat production, a boosted metabolism and reduced hunger. Unfortunately, those assumed sequences of events and their evidence (such as a changed appetite) haven't borne out in research. "That hasn't really held up in the literature at all,” says Heather Seid, a registered dietician who runs the Bionutrition Research Core at the Columbia University Irving Medical Center.

Read More: Forget Dieting. Here's What Really Works to Lose Weight

Instead, there's more scientific support for another physiological mechanism that kicks in on the lowest-of-low-carb meal plans. Called the ketogenic diet, this program was developed by a Mayo Clinic physician for people with epilepsy. The program calls for participants to eat 90 percent of their calories from fat, with very little carbs or protein otherwise. Exactly how the pivot to low-carb, high-fat reduces seizures is not clear.

But the diet does cause weight loss, as it forces the body into ketosis, a metabolic state that digests fat rather than glucose for fuel. People on ketogenic diets lose weight for this reason, but typically gain it back as soon as they stop the program. Additionally, “it’s not fun to eat,” says Seid. Even those with epilepsy might cycle on-and-off the program because it's hard to stick to, she says. “It’s really demoralizing to follow a ketogenic diet for a long period of time.”

Read More: How to Tell If Your Body Is In Ketosis

Research does indicate that low carb regimens can cause some degree of weight loss. For some people, shedding pounds can spark other desirable physical changes. For example, it can help people at risk of developing Type II diabetes — the illness that arises when your body stops producing or responding to insulin. Excess fat likely makes some tissues more resistant to insulin, and if someone can’t generate enough of the hormone to meet that demand, they might develop the disease.

So, when it comes to returning the insulin supply-and-demand to a healthy balance, “weight loss is often that first step,” says Alvarez. For those looking to lose weight for this reason, Alvarez says there’s been some research supporting low-carbohydrate diets as a possible tactic. 

How weight loss happens in these less-stringent low-carb scenarios is still murky. Though often billed as diets that shift insulin production, these programs likely work by initiating a lesser degree of ketosis, Seid says. In fact, going a long time between meals is enough to trigger a little bit of fat-for-fuel burning. It's something our bodies naturally do when running low on food. So if a low-carb diet just encourages participants to eat less overall, then maybe the weight loss comes from reduced-calorie ketosis — not reduced-carb ketosis. This issue surfaced in some of Seid's research.

In their review of research into the efficacy of low-fat and low-carb diets, Seid and her team found that what mattered more than changing diet components was reducing total calories. A lot of research looks at food alterations (like low-carb) while also cutting calories, which makes it hard to pinpoint the cause of someone's smaller pant size, Seid says.

Ideally, a study would only change what people ate, not how much they consumed. In one study, participants — who were consuming pre-set meals — lost more fat on a low-carb diet than they did on a traditional diet, even when both offered the same number of daily calories, Alvarez points out. 

Read More: Can You Reverse Type 2 Diabetes with Diet and Weight Loss?

The challenges of figuring out if (and how) these diets work are broader than just limiting what researchers assess. For one, “low carbohydrate" does not have a single definition. Sure, some more specific programs, like the keto diet, fall under this category, but the larger umbrella includes a range of interpretations. “That to me is one of the biggest issues or questions in our field,” says Alvarez. 

For example, the American Academy of Family Physicians labels a diet “low-carb” if less than 20 percent of the calories come from that nutrient. The Atkins Diet, on the other hand, bases its definition on weight: Those following the program might restrict themselves to 15 to 20 grams of carbohydrates a day for the first couple of weeks. Results across studies are hard to compare when participants adhere to different definitions of the diet. 

At the same time, the various “low-carb” interpretations are helpful, Alvarez says. Not everyone can tolerate sticking to the same, most-restrictive versions. It’s worth knowing if mild carbohydrate reductions also cause weight loss. 

Read More: What Factors Matter Most For Weight Loss?

Low-carb diets come in various plans, and each claim to be key to optimal health and weight loss. 

Cardiologist Dr. Robert C. Atkins developed the diet in the 1960s as a pioneering low-carbohydrate eating plan that restricts carbs while emphasizing protein and fats. The diet progresses through several phases, starting from a very low-carbohydrate induction phase to a lifetime maintenance phase, making it a structured choice for those aiming to change their eating habits permanently.

Riding the waves of 90s health trends, this diet pitches a moderate approach, earmarking about 40 percent of daily energy from carbohydrates. It’s a balancing act of macronutrients aimed at stabilizing blood sugar and controlling hunger.

Channeling the dietary patterns of our Paleolithic ancestors, this diet advocates for a return to basics — high in protein, moderate in fats, and restrained in carbohydrates, particularly the high-glycemic varieties. It's as much about what you eat as it is about echoing ancient human diets.

As a two-phased approach that begins with a strict two-week ban on almost all carbohydrates, the diet transitions into a more relaxed phase allowing roughly 30 percent of daily energy from carbs. It emphasizes low-glycemic index foods to avoid blood sugar spikes.

Though not typically branded as low-carb, the Mediterranean diet naturally leans towards moderate carbohydrate intake, making up about 35 to 40 percent of daily calories. Its heart lies in high-fat foods like olive oil and nuts, alongside an abundance of fruits, vegetables, and lean proteins.

The stringent end of the low-carb spectrum, ketogenic diets drastically reduce carb intake to fewer than 50 grams per day to coax the body into ketosis — a metabolic state where fats, not carbs, fuel the body. It's a diet that not only challenges the body’s metabolic pathways but also the willpower of those who follow it.

Read More: 4 Science-Backed Diets to Improve Your Health

Embarking on a low-carb diet often feels like navigating a culinary maze—what's on the menu and what's off-limits? Primarily, such diets spotlight proteins and a variety of non-starchy vegetables. Think of your plate as a canvas painted mostly with hues of lean meats, fish, and a spectrum of greens from broccoli to bell peppers.

In the realm of low-carb eating, traditional staples like grains, legumes, and fruits take a backseat. Also making fewer appearances are the comfort foods of breads, pastas, and any sweets that dance in your sugar-plum dreams. Starchy vegetables, those underground treasures like potatoes and carrots, are generally sidelined.

Read More: Not Eating Enough Fruits and Veggies Could Kill Millions Every Year

The perfect study scenario is also challenging to sustain. To know exactly what participants eat, dietary research settings ideally supervise people 24/7. Otherwise, the temptations of day-to-day life are too powerful. For example, Seid and her team might try for precise reporting of what people eat during self-supervised meal plans by asking people to bring in their food containers.

“I can’t tell you how many times we receive back wrappers of things that weren’t in the diet,” she says. But complete surveillance studies are expensive, and funding for this kind of research has dried up significantly since the early 2000s. They’re also intimidating to join. Participants get sick of handing all dietary control over to researchers. 

The day might come when dietitians and weight loss researchers all agree about whether all those low-carb options out there do people any good. But in case it never does (or in the meantime), it's important to remember that what you enjoy is likely to work best for you.

When low-carb diets (or really any diet scheme) doesn't result in long-term weight loss, it might be because it’s hard to keep up. Other meal plans, like the Mediterranean Diet, might appeal to people more and bring their own health benefits, Alvarez says. What’s most important is finding what you can stick with.

“What I found in my clinical practice is that finding a diet that is sustainable for a long period of time, where they can have reduced calories and still feel fulfilled and happy, is the most successful diet," Seid says. "And I use 'diet' with quotes around it."

Read More: The Flexible Dieting Lifestyle Could be a Liberating Approach for Losing Weight

Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:

• ispot.tv. Atkins TV Spot, 'Rob Lowe's Little Secret'

• Jessica Alvarez. Registered dietician who studies metabolism and Type II diabetes at the Emory University School of Medicine

• Heather Seid. Registered dietician who runs the Bionutrition Research Core at the Columbia University Irving Medical Center

• Cureus. Advantages and Disadvantages of the Ketogenic Diet: A Review Article

• Journal of Osteopathic Medicine. Are Low-Carbohydrate Diets Safe and Effective?

• Diabetes, metabolic syndrome and obesity: targets and therapy. Mechanism linking diabetes mellitus and obesity

• Nutrients. Low Carbohydrate and Low-Fat Diets: What We Don’t Know and Why We Should Know It

• Metabolism: clinical and experimental. Effects of a eucaloric reduced-carbohydrate diet on body composition and fat distribution in women with PCOS

• Current obesity reports. Benefits of Low Carbohydrate Diets: a Settled Question or Still Controversial?

• Mayo Clinic. Atkins Diet: What's behind the claims?

• Mayo Clinic. Low-carb diet: Can it help you lose weight?