Keto Diet vs. South Beach Diet: Which Is Better?

For many Americans, the typical diet is high in sugar and processed foods, meat and unhealthy fats. But by altering the balance in favor of more healthy fats, lean protein and limiting carbohydrates, many people can quickly shed excess pounds.

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There are several different distinct approaches to reducing carbohydrate intake and increasing healthy fat consumption to lose weight. Among the more popular of these are the keto diet and the South Beach diet. Both approaches promise quick weight loss, but they go about it in somewhat different ways.

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Keto Diet Overview

The keto diet leverages the body’s innate ability to burn fat to fuel activity and weight loss. This is achieved by drastically cutting carbohydrates and increasing the ratio of good fats in the diet. “‘Classic’ keto is a high-fat, adequate protein, low-carbohydrate diet designed to produce ketosis through mimicking the metabolic changes of starvation,” says Cathy Leman, a registered dietitian nutritionist and founder of Dam. Mad. About Breast Cancer, a nutritional consulting firm based in greater Chicago that’s aimed at helping breast cancer patients and survivors. “Keto diets force the body to use fat as its primary source of energy,” she explains.

The approach revolves around a biochemical process called ketosis. Ketosis is when your body breaks down both dietary and stored fat for fuel and creates ketones in the process. Ketones are a byproduct of burning fat that are generated in the liver, and they can be measured in the blood. For people who are looking to follow the keto diet very strictly, you may be testing your blood regularly to track the level of ketones to make sure you’re in the target zone for fat burning.

The keto diet was initially developed in the 1920s as a means of treating severe epilepsy in children. This diet was composed of 90% fat, 6% protein and 4% carbohydrates, which helped to quell epileptic seizures. The diet is still used today in people for whom other treatments haven’t been successful.


If you’re looking to start the keto diet, there are a couple different ways to approach it. You can try to stick with it long term or use it for short-term weight loss. Some people cycle in and out of the program as they need to. The diet features plenty of full-fat dairy, fatty cuts of meat and plenty of nut butter and avocado. It eschews sugars and refined carbohydrates.

The high-fat-very-low-carb ratio can be challenging for some people to meet in day-to-day life, and today there are some slightly more liberal approaches to the keto diet that can boost fat burning by drastically lowering carbohydrate intake. But to be truly a keto diet, the key is to intake a minimal level of carbohydrates and derive most of your daily calories from healthy fats such as avocado and olive oil.

South Beach Diet Overview

With the 2003 publication of his best-selling book, “The South Beach Diet: The Delicious, Doctor-Designed, Foolproof Plan for Fast and Healthy Weight Loss,” cardiologist Arthur Agatston created the South Beach diet. Subsequently, a commercial diet program was also created, and today, people who want to lose weight using this method can use any of the several books written about the approach or sign up with a commercial plan with meal delivery option offered by the company.

The basic premise of the South Beach diet uses a tiered elimination system and a good-bad approach to certain carbohydrates and fats to help dieters shed weight quickly. Dieters start with a 14-day restriction phase, called phase 1, in which bread, pasta, potatoes, rice, baked goods, sweets, ice cream, alcohol, sugar and even fruit are strictly off limits. The idea is to halt sugar dependence and shake up the metabolism to shift the body into a fat-burning mode.


The diet promises to help you drop 8 to 13 pounds in that first two weeks if you follow it to the letter. It also boasts of improved internal health, with a focus on better cardiovascular health.

“You will have corrected the way your body reacts to the very foods that made you overweight,” Agatston explains in his book: “There’s a switch inside you that had been turned on. Now, simply by modifying your diet, you’ll have turned it off. The physical cravings that ruled your eating habits will be gone, and they’ll stay away as long as you stick with the program.”

After that initial two weeks, you can begin adding back some carbohydrates, but only the good ones such as brown rice and some fruits. This phase 2 is designed to be somewhat less restrictive, and dieters will stay in this phase until they reach their goal weight. In this phase, dieters can expect to lose about 1 to 2 pounds per week, which lines up with recommendations from the Centers for Disease Control and Prevention about safe and sustainable weight loss.

The third and final phase of the diet is a “more liberal” maintenance phase intended for dieters who have achieved their desired weight loss, Agatston writes. This phase is intended to be followed long term and looks a bit like a Mediterranean diet with lots of vegetables and fresh fish, lean meats and some dairy.

Across all phases of the diet, the South Beach approach favors inclusion of low-glycemic carbohydrates over high-glycemic carbs. Low-GI carbs do not trigger as intense an insulin response in the body, meaning that they can help you maintain a steady blood sugar level. A steady blood sugar level eliminates spikes and crashes in blood sugar, which can affect energy levels throughout the day.


The diet also emphasizes healthy fats. Instead of unhealthy saturated and trans fats, such as can be found in baked goods, processed meats and French fries, the diet includes healthier monounsaturated fats such as olive oil and avocado. These foods have been linked with positive implications for heart health.

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Health Benefits

Keto diet. Similar to the initial phase of the South Beach diet, the restrictive keto approach can lead to rapid weight loss that can help you combat obesity. Some research has also indicated it can improve hormone balance in some individuals, with less acne and reduction of symptoms associated with polycystic ovary syndrome being associated with this diet in some women.

Studies are also ongoing into whether or not a ketogenic diet can slow the growth of cancer or reduce the risk of cancer recurrence. The idea is that many types of cancer cells thrive when growing in a high-sugar environment. The theory goes that by depriving the body of sugar and forcing it to switch to fat-burning, the growth of cancer cells would slow down or tumors could potentially shrink. Some researchers say that the diet could eventually be considered a form of treatment for certain kinds of cancers when used in conjunction with chemotherapy and other treatments, but definitive answers are still forthcoming.

Because the keto diet features plenty of fat, you may feel less hungry when dieting and consume fewer calories. There have also been some indications that the diet may be able to help with diabetes management, but long-term data is still limited.


South Beach diet. The South Beach diet promises to improve cardiovascular health by reducing body weight, blood pressure and blood lipids (fat and cholesterol in the blood) in those who follow the plan carefully. A reduction of even just 10% of body weight has been proven to have beneficial impacts on the cardiovascular system. Claims that the diet can help control diabetes still lack hard evidence, but a reduction in body weight has been linked to improved symptoms in some people.

Registered dietitian and certified sports nutritionist Shawn Wells, based in the Dallas/Fort Worth-area, says one of the pros of the South Beach diet is that it forces people to become “conscious of your food intake,” while emphasizing fresh, whole foods, “which is optimal.” He also likes the phased approach to the diet, “as these phases allow for progress as you are on the diet.”

Wells says that both diets “limit carbohydrates in the form of processed carbs, making them naturally low in processed, high sugar foods. So either way, people will gain health benefits from them,” if you’re coming from a high-sugar diet. He also notes that the South Beach diet “is more of a ‘diet,’ whereas keto is more of a ‘lifestyle’ that elicits ketosis and the ability to use ketones as fuel, for weight loss, cognitive and various other benefits. Both are logical and likely to be beneficial to people’s health.”

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Health Risks

Keto. A common complaint among people who have recently switched to a keto diet is the so-called keto flu. This is a series of symptoms including fatigue, headaches, muscle aches and gastrointestinal distress that usually passes within a few days. It’s triggered by the body switching to burning fat, and during the week or so that people commonly experience this keto flu, it can be tough to keep up athletic performance and feel normal. Plenty of sleep and hydration can help you get over the keto flu a little faster.

Because the keto diet is restrictive, “anyone struggling with an eating disorder, pregnant or nursing women, patients with kidney disease and people on medication that lowers blood sugar should exercise caution and get supervision,” Leman says. In addition, “research on long-term effects of the keto diet is underway, but as of now, data is lacking.” People who are diabetic may also want to avoid the keto diet, or follow it only under the close supervision of a doctor or a dietitian with special training in diabetes management.

Wells notes that some people following the keto diet get too caught up in tracking macronutrient ratios and don’t spend enough energy looking for high-quality food. So these individuals “tend to eat poor-quality, processed fats, which will show results in the short-term but can lead to serious health issues in the long term. This is called ‘dirty keto’ and should be avoided,” which means processed meat products and artificial sweeteners should be limited. “Keto diets should be focused on whole food sources to ensure that the large amount of fats are coming from natural, undamaged sources,” he explains.

South Beach. The South Beach diet can also be quite restrictive, especially in the first few weeks. But as you progress through the phases, you’ll be able to incorporate more food items, and the diet begins to look a bit more like a Mediterranean diet, which is considered a healthy lifestyle more than just a diet. As with most other diets for weight loss, it’s best for kids to avoid the South Beach diet.

Wells also cautions against becoming “‘fat-phobic, where you are avoiding fats,” which some people do when trying to cut calories. He points to another widely acclaimed approach to eating for inspiration, the Mediterranean diet. “That’s a very healthy diet. It’s high in fat, and so limiting fat may not be the healthiest option.”

Costs

The costs for a do-it-yourself approach to either the keto diet or the South Beach diet are likely to be similar. Both diets rely on fat and protein for the bulk of calories, and carbohydrate sources tend to be less expensive, so both diets can get pricey. Wells notes that because the South Beach diet tends to include more meat, it can also be a little more expensive than a strict keto diet. “It has certain food requirements, which limits flexibility and tends to be more expensive,” he says.

If you go the commercial route with the South Beach diet, you can expect to spend about $300 to $380 per month for meal delivery, depending on the plan. This approach takes much of the guesswork out of sticking with the diet, but may be less budget-friendly than purchasing your own groceries and cooking your own meals.

Which Is Better?

Because the South Beach diet and the keto diet share many similarities in their low-carb approach to weight loss, it’s difficult to pick a clear winner. In fact, the South Beach diet advertises keto-friendly options.

For fast weight loss, both diets offer a similar proposition. Longer term maintenance of weight loss and sticking to either diet as a lifestyle can be challenging for many people.

In U.S. News’ 2019 Best Diets rankings, the South Beach diet tied for No. 20 overall (out of 41). For weight loss, it tied for 17th place. The keto diet tied for 38th place overall. For weight loss, it did a little better, tying for 12th place in the Best Weight-Loss Diets category.

For those who would prefer the support of a commercial weight plan, the South Beach diet company offers such. For those who want to do meal planning and prep on their own, either the South Beach or keto approach can work.

“I like the idea of the three phases of the South Beach diet,” Wells says, “which focuses on reintroducing foods as you become more dialed in with your nutrition.” That said, he tends to recommend the keto approach more, but emphasizes that you should focus on a clean, whole foods version of the diet rather than processed or prepackaged foods. He also prefers a phased or cyclical approach to keto. “As you become more in tune with your nutrition and achieve some weight loss goals you can become more flexible and add foods back in, in phases. Long term, keto is a better option in my opinion.”

In people with difficult-to-manage diabetes, ketoacidosis is possible, a dangerous complication of diabetes when blood sugar and ketone levels are too high. 

May help prevent or slow cancer.

Shown to control epilepsy in some children.

Elaine K. Howley, Contributor

Elaine Howley began writing for U.S. News in 2017, covering breast cancer and COPD. Since …  Read more

Sources

Cathy Leman, RDN; Shawn Wells, MPH, LDN, RD, CISSN

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