Ask Stew: Does a Keto Diet or Fasting Work Best?

Eating right mix of fats, carbs and proteins is key to a ketogenic diet.
The key to the ketogenic diet is to eat a balance of about 75% quality fat, 20% protein and 5% carbohydrates, according to diet experts. (Eric Pilgrim/Fort Knox)

Diet fads come and go, but what actually works? Some diets have scientific basis behind them, but many do not. Understanding diet and nutritional choices is a full-time job and I am not a nutritionist, so finding what works and why it works is always part of the challenge as a fitness writer.

My go-to answers are in the form of scientific studies as well as opinions of nutritionists and registered dietitians (see list below). But here is a question that is tough to answer as it pushes outside my comfort zone, but I do have personal experience and links to studies for you to consume:


Now in my late 40s, I am looking at losing weight. I need to -- actually. I have come to the age where outworking my diet (like you say) is not in the cards, so my intake needs to change. I have been reading about intermittent fasting and ketosis diet planning. Do you have a recommendation on either or a different one perhaps?  Jason

My experience (one month of ketosis):

It took nearly a week to get into ketosis, which occurs when the body doesn't have enough carbohydrates to use for energy. During that week of checking with keto urinalysis strips, I lost three pounds not because I was in ketosis, but because I took out 30%-40% of my daily calories from carbohydrates (breads, grains, snacks, juice), though I ate tangerines, broccoli and asparagus to the tune of about 50 grams of carbs in a day. Still the reduction in calories per day caused the weight loss, not ketosis.

Once in ketosis for about three weeks, weight loss continued to occur. However, one day on a fat and protein binge (steak and chicken), I took in about 5,000 calories that day. I did not burn off that many calories that day, so the result was a calorie surplus and weight gain regardless of ketosis. It took another 36-48 hours before I was losing weight again -- even though in ketosis. So you cannot eat all the protein and fat you want, because your body still has to metabolize what it consumes. Moderation and portion control still play important roles.

Energy to work out

Early-morning workouts on a low-carb diet required some backup carbs to "stay in the game;" sipping about 15-20 grams of carbs in Gatorade helped with the lightheaded effect. Or you can drop the intensity and do some lower-impact cardio and avoid the carbs if you prefer. But after about 30 minutes of normal workout activity, dropping the workout to lower impact/lower heart rate (less than 120 beats per minute) was helpful to staying active (swimming, slow jog/walk and biking).

Here is the thing about fasting/lower-carb diets from my experience:

Portion control: A diet that creates a caloric deficit will work for reducing body fat. You do not have to be in ketosis to lose fat. You still can eat carbs, proteins and fats, but if you control portion size and create the deficit by eating less and moving more, you will lose weight.

Fasting options: Fasting is not the optimal method to weight loss, but it can work temporarily if you do not mind getting "hangry" and lack energy to train or think, for that matter. "Intermittent fasting" has become popular; it allows for a particular time of day to eat, then the rest of the day/night, you avoid food altogether. This one requires discipline, like most diets, but it can work for some. At the end of the day, it truly comes down to you having eaten less than normal -- creating that caloric deficit. In fact, fasting can be detrimental to muscle growth (catabolic) so consider carefully how you implement this one.

My recommendation is to see whether you like them. I am a big fan of reducing, if not completely (almost) eliminating, sugar from a diet. I think too much sugar is a health risk too many people do not realize. So start with reducing sugar, drink more water, eat smaller portions and exercise for 30 minutes a day.

References and related articles:

Stew Smith is a former Navy SEAL and fitness author certified as a Strength and Conditioning Specialist (CSCS) with the National Strength and Conditioning Association. Visit his Fitness eBook store if you're looking to start a workout program to create a healthy lifestyle. Send your fitness questions to

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Fitness Diet and Nutrition