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Are keto, paleo and other fad diets safe?

January 04, 2018 | Katie Rankell, RD, CDE
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The New Year offers a fresh start just when we are most motivated and eager to tackle any extra weight we’ve gained. But which diet regimen is best?

Friends and influencers may promote keto, paleo, raw food or other diets among the multitudes to choose from. But when you are considering a trending or popular weight-loss regimen, know that a “good” diet is one that has been around for a while.

As a dietitian with the UCI Health Weight Management Program, I tell my patients that effective diets have lots of evidence-based research to support them, such as a Mediterranean diet or a vegetarian diet.

Fad diets, on the other hand, tend to be short-term, have little or no evidence behind them, are touted in magazines then fall off the public’s radar. That doesn’t necessarily mean they should be completely dismissed, however.

Let’s take a closer look at some current popular diets:

Paleo Diet

The idea behind the paleo diet is that it is supposed to mimic our hunter/gatherer ancestors. The diet is focused on whole, unprocessed foods.

  • Pros: It emphasizes eliminating processed foods, which means cutting a lot of fast foods and convenience foods. Eating unprocessed foods is generally going to be healthier, but you still need to control portion size and to make sure you are getting a balance from important food groups. You’ll also need to read food labels to ensure that ingredients truly are unprocessed.
  • Cons: The paleo diet has no clear guidelines: The main focus is on whole, unprocessed foods. But one person on the diet could choose a mix of low-carb and high-fat foods with more animal products, while someone else could have a high-carb, low-fat diet with more whole grains, fruits and vegetables.

Low-Carb Diets (Keto or Ketogenic Diet, Atkins Diet, South Beach Diet, The Whole 30 Diet)

Low-carb diets focus on decreasing the consumption of carbohydrates by varying amounts and on eating more foods high in fat and protein to promote burning fat as fuel, instead of glucose found in carbohydrates. Each of these low-carbohydrate diets have their own prescription for how many carbs are allowed, but they all call for less than the U.S. Department of Agriculture (USDA) recommends for daily carbohydrate intake.

USDA Dietary Guidelines recommend that 45 percent to 65 percent of total calories come from carbohydrates. Ketogenic diets, for example, recommend no more than 5 percent carbs.

  • Pros: Low-carb diets do typically result in weight loss and they can help pre-diabetic or diabetic patients lower their insulin levels. However, the big question is always, is it a diet that is sustainable for the long-term.
  • Cons: Low-carb diets tend to be higher in fat and can raise cholesterol levels. They also can be risky for heart patients to follow, and they tend to lack beneficial fiber.

The Zone Diet

Although the Zone diet is technically a low-carb diet, it calls for only slightly less carbohydrates than the USDA recommends. Zone diet meals are supposed to be 40 percent carbs, 30 percent protein and 30 percent fat.

  • Pros: No food is off limits on this diet and it allows snacks. It is also simple to follow: One-third of the plate should have lean protein; the other two-thirds of the plate should include complex carbohydrates with a little healthy fat, such as nuts or avocados. For people trying to lose weight and lower blood sugar, this regimen may work well.
  • Cons: These nutrient breakdowns may not be realistic for people long-term. Also, since the fat recommendations are a little higher than average, it may not be the best diet for people with high cholesterol and/or heart issues.


Defining a cleansing diet is difficult because they vary widely. Cleanses tend to be short-term regimens and their proponents make a variety of health claims, such as that they will improve energy or eliminate toxins. Some cleanses include fasting, others can be liquids only. Still others are smoothies or include supplements that claim to eliminate toxins. 

  • Pros: I don’t see any pros to cleanses. Toxins are removed from our bodies naturally by our liver and through our urine, feces and sweat.
  • Cons: There are no standards or guidelines, so cleanses put people at risk for low blood sugar and/or dehydration. Supplements and herbs can be harmful if not monitored properly by a healthcare professional.

Raw Diet

As its name suggests, this diet consists of entirely raw foods or mostly raw foods, including foods that are heated to no more than 118 degrees to prevent nutrient alterations caused by cooking. 

  • Pros: This diet eliminates animal products and fats, so it could help someone who needs to reduce their cholesterol. 
  • Cons: This is a major elimination diet. It also makes it hard to get enough protein, which means that people who follow this regimen may need B12 supplements that can only be obtained from animal food sources. A person following the diet also risks ingesting harmful bacteria or cross contamination by not cooking foods at high enough temperatures. In addition, raw foods put a lot of stress on the digestive system, so this would not be a good option for people with irritable bowel syndrome (IBS) or other digestive health issues.

Macrobiotic Diet

This diet used to be very restrictive because it was based heavily on brown rice and water. However, it has grown more expansive and now includes some seafood, nuts, seeds, legumes and other grains.

  • Pros: It’s a low-fat diet, so it could help people with high cholesterol and/or heart problems.
  • Cons: As a high-carb diet, a macrobiotic diet would not be good for pre-diabetics and diabetics, and it would be unlikely to result in weight loss. Again, I question its sustainability because it is highly restrictive.

Gluten-Free Diet and/or Dairy-Free Diet

The gluten-free diet was originally designed for people with celiac disease, a condition in which the body cannot break down and digest gluten. Gluten is found in many grains, especially ones we use a lot in the United States, like wheat, barley and rye. However, more people without celiac disease are using the diet because it cuts out a lot of common carbohydrates found in Western diets.

Similarly, a dairy-free diet was designed for people with lactose intolerance or allergens to dairy. It has become a more popular diet among people without these conditions who are looking to reduce their saturated fat intake as well as potentially reduce inflammation.

  • Pros: A gluten-free diet can be a healthy well-balanced diet. For people who are sensitive to gluten, following this diet may improve bowel or digestive conditions and reduce intestinal discomfort and bloating. Similarly, for people who are sensitive to dairy, it may improve gas, bloating and skin conditions.
  • Cons: If you don’t have allergies or are not sensitive to gluten or dairy, there’s no reason to eliminate foods if you don’t have to. If you remove certain food groups, such as dairy, and replace them with something else, the result may not be as healthy or balanced. Also, if you eliminate dairy, you may need to supplement with calcium.

A dietitian’s view

From my standpoint, a balanced diet is a healthy diet:

  • You need good carbs (complex carbohydrates, such as quinoa or oatmeal; not refined carbohydrates, such as crackers and chips)
  • You need protein (lean meats, like fish and chicken; not red meats or processed meats)
  • And you need fat (mono-unsaturated fats, like avocados and olive oil; not saturated fats like butter and red meat)

If you eliminate foods you really enjoy, chances are you are going to be white-knuckling your way through the diet. Most of us can only white-knuckle something for so long. Deprivation usually leads to binging, which typically puts lost pounds back on and then some.

No. 1 indicator of weight loss success

Yo-yo dieting is the biggest thing to avoid because when you lose weight, you lose muscle mass as well as fat. Then when you gain back the weight you lost, it returns as all fat, so now your body composition is even worse off than before. The best way to keep extra weight off is by following some sort of maintenance program for at least a year. 

In fact, the No. 1 indicator of success is a willingness to be held accountable, even more so than physical exercise.

No matter what diet you choose, it’s a good idea to work with a licensed registered dietitian and to commit to a year of accountability after you reach your desired goal weight to help yourself keep it off permanently. 

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