A woman wearing a yellow apron tosses a salad in a wooden bowl.

Remember grapefruit-binging to lose weight? That plan turned sour like so many gimmicky diets du jour, from the too-tempting-to-be-good all-chocolate diet (OK, we made that up) to alternate-day fasting.

So which popular plans excel and which flop? We got the skinny on the diets’ effectiveness, speed, sustainability and healthiness from Chelsea Johnson, RD., LD, Outpatient and Bariatric Dietitian at Memorial Hermann Memorial City Medical Center.

Ketogenic Diet

Scoop: Steak, sausage, cheese, baloney – and dropped pounds -- what’s not to like? The goal of a very high-fat, low-carbohydrates regimen is to starve the body of consumed carbs, forcing it to burn its own fat instead.

Insider Tip: This diet gets its name from the buildup of acids known as ketones – a sign of crisis from a body struggling to compensate for missing nutrients.

Results Speed: 1-2 days, and 10 pounds within the first month.

Lifespan: Your foggy brain craves carbs for clarity. Weight loss stops, and, with it, any motivation. “When you go back to old habits, the weight comes back,” Johnson says.

Risks: High-fat intake stresses the liver and can spike cholesterol levels, while robbing the body of vital vitamins and minerals.

As with all diets, calories ingested and expended matter most.

Grade: “I’d give it a D – for dangerous,” Johnson says. “If it didn’t work at first, I’d give it an F.”

Alternate-Day Fasts

Scoop: Two approaches exist for this regimen. For one, you eat only within a six- to eight-hour window daily. The other lets you eat normally five days a week, with two days weekly of less than 500 calories each

Insider Tip: As with all diets, calories ingested and expended matter most. “Calorie reduction can make fasts work, not the timing of when you eat,” Johnson says.

Results Speed: 1-2 weeks.

Lifespan: Fasts are sustainable – if you eat moderately and healthily when you eat and don’t binge on non-fasting days.

Risks: Lack of food can cause dizziness, nausea and fatigue. Studies suggest fasts may slow metabolism and possibly harm your heart.

Grade: B.


Scoop: Gluten, a protein in wheat, barley and rye, gives some people digestive issues, including colitis and celiac disease.

Insider Tip: “Gluten-free isn’t always healthier,” Johnson says. “A cookie is a cookie. If you simply replace packaged foods with gluten-free versions, you won’t lose weight.”

Results Speed: 2-4 weeks. “But it’s not the absent gluten that’s causing weight loss,” Johnson says. “If you cut out bread, pasta, cakes, cookies and sweets, you’re eating less.”

Lifespan: If you have a gluten intolerance or allergy, you’ll feel better and be motivated to continue the diet, she says.

Risks: Foods rich in gluten also tout iron, vitamin B12 and zinc, so a dietician or doctor can help you get nutrients.

Grade: B. “If you don’t have a medical condition,” Johnson says, “dropping gluten isn’t necessary.”

Plant-Based Diet

Scoop: This diet works from the ground up, with 90% of the menu being whole, natural and unprocessed fruits, veggies, beans, nuts and seeds. Carving away meat and dairy makes it almost the reverse of ketogenic regimens. You don’t have to be a vegetarian (no meat) or vegan (also no eggs or dairy) as long as 90% of your diet is plant-based, Johnson says.

Insider Tip: “Gradual changes reap bigger results over time,” she says. So add 2-3 servings of veggies and fruits daily, while whittling meat to 1-2 servings weekly. And be honest with yourself: “Technically, French fries may be from a plant – potato – but they’re still fatty and caloric,” she says.

Results Speed: A week or two. “But if you’re eating the same amount of calories, your weight will stay the same.”

Lifespan: Since you’re adding rather than eliminating foods, you don’t feel as deprived, Johnson says. “You’ll also feel better, which makes it easier to sustain.”

Risks: “Check with your doctor,” she says. “If you completely avoid meat or dairy, you might have vitamin deficiencies.”

Grade: “If done correctly I’d give this one an A,” Johnson says.


Chelsea Johnson,
MH outpatient dietician. RD

Chelsea Cappelle Johnson MS, RD, LD
Outpatient Dietitian/Bariatric Dietitian

Get Your Daily Dose of Health & Wellness

Sign up to receive the latest articles in your inbox.

A woman in climbing gear looks up at a climbing rock wall.


Hate Running? Here Are 5 Unconventional Ways to Work Out

Read More
A plate surrounded by slices of fruits and vegetables.


I'm a Dietitian. Here's What I Eat in a Day

Read More