Updated: Sep 20, 2019
There are many weight loss diets out there.
Some focus on reducing your appetite, while others restrict calories, carbs, or fat.
Since all of them claim to be superior, it can be hard to know which ones are worth trying.
The truth is that no one diet is best for everyone — and what works for you may not work for someone else.
This article reviews the 9 most popular weight loss diets and the science behind them.
1. The Paleo Diet
The paleo diet claims that you should eat the same foods that your hunter-gatherer ancestors ate before agriculture developed.
The theory is that most modern diseases can be linked to the Western diet and the consumption of grains, dairy, and processed foods.
While it's debatable whether this diet really provides the same foods your ancestors ate, it is linked to several impressive health benefits.
How it works: The paleo diet emphasizes whole foods, lean protein, vegetables, fruits, nuts, and seeds, while discouraging processed foods, sugar, dairy, and grains.
Some more flexible versions of the paleo diet also allow for dairy like cheese and butter, as well as tubers like potatoes and sweet potatoes.
Weight loss: Several studies have shown that the paleo diet can lead to significant weight loss and reduced waist size.
In studies, paleo dieters automatically eat much fewer carbs, more protein, and 300–900 fewer calories per day.
Other benefits: The diet seems effective at reducing risk factors for heart disease, such as cholesterol, blood sugar, blood triglycerides, and blood pressure.
The downside: The paleo diet eliminates whole grains, legumes, and dairy, which are healthy and nutritious.
SUMMARY: The paleo diet emphasizes whole foods but bans grains and dairy. Its multiple health benefits include weight loss.
2. The Vegan Diet
The vegan diet restricts all animal products for ethical, environmental, or health reasons.
Veganism is also associated with resistance to animal exploitation and cruelty.
How it works: Veganism is the strictest form of vegetarianism.
In addition to eliminating meat, it eliminates dairy, eggs, and animal-derived products, such as gelatin, honey, albumin, whey, casein, and some forms of vitamin D3.
Weight loss: A vegan diet seems to be very effective at helping people lose weight — often without counting calories — because its very low fat and high fiber content may make you feel fuller for longer.
Vegan diets are consistently linked to lower body weight and body mass index (BMI) compared to other diets.
One 18-week study showed that people on a vegan diet lost 9.3 pounds (4.2 kg) more than those on a control diet. The vegan group was allowed to eat until fullness, but the control group had to restrict calories.
However, calorie for calorie, vegan diets are not more effective for weight loss than other diets.
Weight loss on vegan diets is primarily associated with reduced calorie intake.
Other benefits: Plant-based diets are linked to a reduced risk of heart disease, type 2 diabetes, and premature death.
Limiting processed meat may also reduce your risk of Alzheimer's disease and dying from heart disease or cancer.
The downside: Because vegan diets eliminate animal foods completely, they may be low in several nutrients, including vitamin B12, vitamin D, iodine, iron, calcium, zinc, and omega-3 fatty acids.
SUMMARY: Vegan diets exclude all animal products. They may cause weight loss due to lower calorie intake while reducing your risk of several diseases.
3. Low-Carb Diets
Low-carb diets have been popular for decades — especially for weight loss.
There are several types of low-carb diets, but all involve limiting carb intake to 20–150 grams per day.
The primary aim of the diet is to force your body to use more fats for fuel instead of using carbs as a main source of energy.
How it works: Low-carb diets emphasize unlimited amounts of protein and fat while severely limiting your carb intake.
When carb intake is very low, fatty acids are moved into your blood and transported to your liver, where some of them are turned into ketones.
Your body can then use fatty acids and ketones in the absence of carbs as its primary energy source.
Weight loss: Numerous studies indicate that low-carb diets are extremely helpful for weight loss, especially in overweight and obese individuals.
They seem to be very effective at reducing dangerous belly fat, which can become lodged around your organs.
People on very low-carb diets commonly reach a state called ketosis. Many studies note that ketogenic diets lead to more than twice the weight loss than a low-fat, calorie-restricted diet.
Other benefits: Low-carb diets tend to reduce your appetite and make you feel less hungry, leading to an automatic reduction in calorie intake.
Furthermore, low-carb diets may benefit many major disease risk factors, such as blood triglycerides, cholesterol levels, blood sugar levels, insulin levels, and blood pressure.
The downside: Low-carb diets do not suit everyone. Some feel great on them while others feel miserable.
Some people may experience an increase in “bad” LDL cholesterol.
In extremely rare cases, very low-carb diets can cause a serious condition called ketoacidosis. This condition seems to be more common in lactating women and can be fatal if left untreated.
However, low-carb diets are safe for the majority of people.
SUMMARY: Low-carb diets severely limit carb intake and push your body to use fat for fuel. They aid weight loss and are linked to many other health benefits
4. The Dukan Diet
The Dukan diet is a high-protein, low-carb weight loss diet split into four phases — two weight loss phases and two maintenance phases.
How long you stay in each phase depends on how much weight you need to lose. Each phase has its own dietary pattern.
How it works: The weight loss phases are primarily based on eating unlimited high-protein foods and mandatory oat bran.
The other phases involve adding non-starchy vegetables followed by some carbs and fat. Later on, there will be fewer and fewer pure protein days to maintain your new weight.
Weight loss: In one study, women following the Dukan diet ate about 1,000 calories and 100 grams of protein per day and lost an average of 33 pounds (15 kg) in 8–10 weeks.
Also, many other studies show that high-protein, low-carb diets may have major weight loss benefits.
These include a higher metabolic rate, a decrease in the hunger hormone ghrelin and an increase in several fullness hormones.
Other benefits: Apart from weight loss, there are no recorded benefits of the Dukan diet in scientific literature.
The downside: There is very little quality research available on the Dukan diet.
The Dukan diet limits both fat and carbs — a strategy not based on science. On the contrary, consuming fat as part of a high-protein diet seems to increase metabolic rate compared to both low-carb and low-fat diets.
What’s more, fast weight loss achieved by severe calorie restriction tends to cause significant muscle loss.
The loss of muscle mass and severe calorie restriction may also cause your body to conserve energy, making it very easy to regain the weight after losing it.
SUMMARY: The Dukan diet has not been tested in quality human studies. The diet may cause weight loss, but it also may slow down your metabolism and make you lose muscle mass along with fat mass.
5. The Ultra-Low-Fat Diet
An ultra-low-fat diet restricts your consumption of fat to under 10% of daily calories.
Generally, a low-fat diet provides around 30% of its calories as fat.
Studies reveal that this diet is ineffective for weight loss in the long term.
Proponents of the ultra-low-fat diet claim that traditional low-fat diets are not low enough in fat and that fat intake needs to stay under 10% of total calories to produce health benefits and weight loss.
How it works: An ultra-low-fat diet contains 10% or fewer calories from fat. The diet is mostly plant-based and has a limited intake of animal products.
Therefore, it's generally very high in carbs — around 80% of calories — and low in protein — at 10% of calories.
Weight loss: This diet has proven very successful for weight loss among obese individuals. In one study, obese individuals lost an average of 140 pounds (63 kg) on an ultra-low-fat diet.
Another 8-week study with a diet containing 7–14% fat showed an average weight loss of 14.8 pounds (6.7 kg).
Other benefits: Studies suggest that ultra-low-fat diets can improve several risk factors for heart disease, including high blood pressure, high cholesterol, and markers of inflammation.
Surprisingly, this high-carb, low-fat diet can also lead to significant improvements in type 2 diabetes.
Furthermore, it may slow the progression of multiple sclerosis — an autoimmune disease that affects your brain, spinal cord, and optic nerves in the eyes.
The downside: The fat restriction may cause long-term problems, as fat plays many important roles in your body. These include helping build cell membranes and hormones, as well as helping your body absorb fat-soluble vitamins.
Moreover, an ultra-low-fat diet limits intake of many healthy foods, lacks variety, and is extremely hard to stick to.
SUMMARY: An ultra-low-fat diet contains less than 10% of its calories from fat. It can cause significant weight loss and may also have impressive benefits for heart disease, type 2 diabetes, and multiple sclerosis.
6. The Atkins Diet
The Atkins diet is the most well-known low-carb weight loss diet.
Its proponents insist that you can lose weight by eating as much protein and fat as you like, as long as you avoid carbs.
The main reason why low-carb diets are so effective for weight loss is that they reduce your appetite.
This causes you to eat fewer calories without having to think about it.
How it works: The Atkins diet is split into four phases. It starts with an induction phase, during which you eat under 20 grams of carbs per day for two weeks.
The other phases involve slowly reintroducing healthy carbs back into your diet as you approach your goal weight.
Weight loss: The Atkins diet has been studied extensively and found to lead to faster weight loss than low-fat diets.
Other studies note that low-carb diets are very helpful for weight loss. They are especially successful in reducing belly fat, the most dangerous fat that lodges itself in your abdominal cavity.
Other benefits: Numerous studies show that low-carb diets, like the Atkins diet, may reduce many risk factors for disease, including blood triglycerides, cholesterol, blood sugar, insulin, and blood pressure.
Compared to other weight loss diets, low-carb diets also better improve blood sugar, “good” HDL cholesterol, triglycerides, and other health markers.
The downside: As do other very low-carb diets, the Atkins diet is safe and healthy for most people but may cause problems in rare cases.
SUMMARY: The Atkins diet is a low-carb weight loss diet. It's effective for weight loss but also has benefits for many other disease risk factors.
7. The HCG Diet
The HCG diet is an extreme diet meant to cause very fast weight loss of up to 1–2 pounds (0.45–1 kg) per day.
Its proponents claim that it boosts metabolism and fat loss without inducing hunger.
HCG (human chorionic gonadotropin) is a hormone present at high levels during early pregnancy.
It tells a woman's body it's pregnant and maintains the production of hormones that are important for fetal development. It has also been used to treat fertility issues.
How it works: The diet is split into three phases. During the first phase, you begin taking HCG supplements.
During the second phase, you follow an ultra-low-calorie diet of only 500 calories per day, along with HCG supplement drops, pellets, injections, or sprays. The weight loss phase is prescribed for 3–6 weeks at a time.
In the third phase, you stop taking HCG and slowly increase your food intake.
Weight loss: The HCG diet does cause weight loss, but multiple studies conclude that the weight loss is due to the ultra-low-calorie diet alone — not the HCG hormone.
Furthermore, HCG was not found to reduce hunger.
Other benefits: Aside from weight loss, there are no documented benefits of the HCG diet.
The downside: Like most other ultra-low-calorie diets, the HCG diet may cause muscle loss, which results in a reduced ability to burn calories.
Such severe calorie restriction further reduces the number of calories your body burns. This is because your body thinks it's starving and therefore attempts to preserve energy.
In addition, most HCG products on the market are scams and don't contain any HCG. Only injections are able to raise blood levels of this hormone.
Moreover, the diet has many side effects, including headaches, fatigue, and depression.
There is also one report of a woman developing blood clots, most likely caused by the diet.
The FDA disapproves of this diet, labeling it dangerous, illegal, and fraudulent.
SUMMARY: The HCG diet is a rapid weight loss diet. It's not based on any scientific evidence and may reduce metabolic rate and cause muscle loss, headaches, fatigue, and depression.
8. The Zone Diet
The Zone Diet is a low-glycemic load diet that has you limit carbs to 35–45% of daily calories and protein and fat to 30% each.
It recommends eating only carbs with a low glycemic index (GI).
The GI of a food is an estimate of how much it raises your blood glucose levels after consumption.
The Zone Diet was initially developed to reduce diet-induced inflammation, cause weight loss, and reduce your risk of chronic diseases.
How it works: The Zone Diet recommends balancing each meal with 1/3 protein, 2/3 colorful fruits and veggies, and a dash of fat — namely monounsaturated oil, such as olive oil, avocado, or almonds.
It also limits high-GI carbs, such as bananas, rice, and potatoes.
Weight loss: Studies on low-GI diets are rather inconsistent. While some say that the diet promotes weight loss and reduces appetite, others show very little weight loss compared to other diets.
Other benefits: The greatest benefit of this diet is a reduction in risk factors for heart disease, such as reduced cholesterol and triglycerides.
One study suggests that the Zone Diet may improve blood sugar control, reduce waist circumference, and lower chronic inflammation in overweight or obese individuals with type 2 diabetes.
The downside: One of the few drawbacks of this diet is that it limits the consumption of some healthy carb sources, such as bananas and potatoes.
SUMMARY: The Zone Diet is a low-GI diet. Studies on its weight loss benefits are inconsistent, but the diet improves many important health markers and reduces your risk of heart disease.
9. Intermittent Fasting
Intermittent fasting cycles your body between periods of fasting and eating.
Rather than restricting the foods you eat, it controls when you eat them. Thus, it can be seen as more of an eating pattern than a diet.
The most popular ways to do intermittent fasting are:
The 16/8 method: Involves skipping breakfast and restricting your daily eating period to eight hours, frequently fasting for the remaining 16 hours of the day.
The eat-stop-eat method: Involves 24-hour fasts once or twice per week on non-consecutive days.
The 5:2 diet: On two non-consecutive days of the week, you restrict your intake to 500–600 calories. You do not restrict intake on the five remaining days.
The Warrior Diet: Eat small amounts of raw fruits and vegetables during the day and one huge meal at night.
How it works: Intermittent fasting is commonly used for weight loss because it leads to relatively easy calorie restriction.
It can make you eat fewer calories overall — as long as you don't overcompensate by eating much more during the eating periods.
Weight loss: Intermittent fasting is generally very successful for weight loss. It has been shown to cause weight loss of 3–8% over a period of 3–24 weeks, which is a lot compared to most weight loss diets.
In addition to causing less muscle loss than standard calorie restriction, it may increase your metabolic rate by 3.6–14% in the short term.
Other benefits: Intermittent fasting may reduce markers of inflammation, cholesterol levels, blood triglycerides, and blood sugar levels.
Furthermore, intermittent fasting has been linked to increased levels of human growth hormone (HGH), improved insulin sensitivity, improved cellular repair, and altered gene expressions.
Animal studies also suggest that it may help new brain cells grow, lengthen lifespan, and protect against Alzheimer's disease and cancer.
The downside: Although intermittent fasting is safe for well-nourished and healthy people, it does not suit everyone.
Some studies note that it's not as beneficial for women as it is for men.
In addition, some people should avoid fasting, including those sensitive to drops in blood sugar levels, pregnant women, breastfeeding moms, teenagers, children, and people who are malnourished, underweight, or nutrient deficient.
SUMMARY: Intermittent fasting lets your body cycle between fasting and eating. It is very effective for weight loss and has been linked to numerous health benefits.
The Bottom Line
There is no perfect weight loss diet.
Different diets work for different people, and you should pick one that suits your lifestyle and tastes.
The best diet for you is the one that you can stick to in the long term.
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