Start searching for information about a vegan diet, and you’ll quickly uncover two (alleged) benefits of an animal food-free diet—at least according to the so-called dietary experts:

  • Fat consumption. A vegan diet makes it easier to stay within the 25% to 35% of daily calories from fat that dieticians recommend. Supposedly, you’ll be eating healthier unsaturated fats from avocados, nuts and vegetable oils, so you’ve got that going for you—if you believe fat is evil.
  • Weight loss. According to conventional nutritionists who’ve reviewed vegan diets, you are “likely” to lose weight, because you’ll be eating fewer calories, while consuming more fruits, veggies and whole grains. Thanks to that daily caloric deficit, “You’re bound to shed the pounds,” as U.S. News & World Report’s Health website phrased it.

We’ll deal with the fat intake assertion in a moment, but let’s first discuss losing weight on a vegan diet.

The assertion that weight loss is inevitable on a diet that delivers a daily caloric deficit—eating fewer calories than your body needs to maintain its basal metabolism and normal activity levels—is correct. It’s called starvation, and from famines in Africa to horror stories of concentration camps, there’s no shortage of imagery to visualize the end point of a “caloric deficit diet.”

That’s because when the body is deprived of the energy sources (and protein intake) it needs to function properly, body tissues are catabolized to make up the deficit. Yes, that involves using up stored subcutaneous fat, but it also includes the breakdown of muscle tissue, which is why famine victims appear to be wasting away.

Because they are.

Do they lose weight? Heck, yeah.

Is it healthy? Absolutely not.

Weight management is important for a variety of clinical (and aesthetic) reasons, but the way to do it doesn’t involve depriving yourself of needed calories—even a relatively small deficit—over time. In fact, that’s the exact and specific cause of “yo-yo-dieting,” a syndrome way too many overweight people have endured: You starve yourself for weeks, maybe months, until you lose a lot of weight (keep in mind, the loss is both fat and muscle tissue).

Then, after finally reaching a more desirable weight, you resume “normal” eating patterns and calorie intake. What happens?

Since you’ve lost significant muscle mass, your metabolism is slower and you’re burning fewer calories at rest. So the resumption of your previous diet means you regain the lost weight—with a vengeance. Now, the next time you try to lose weight with restrictive dieting, it’s much more challenging, and the yo-yo process repeats itself with even worse results.

So in case you’re considering shedding some pounds by consuming fewer calories than you actually need, a word of advice: Don’t!

The fat fallacy

Now, about the idea that fat reduction—specifically saturated fat—is a wonderful side effect of a vegan diet.

It’s not.

There has been plenty of discussion in this space about the need for fat and cholesterol, especially for growing children. Nutritionally, it’s essential for nervous system development, proper cell metabolism and a host of other biological functions we can’t manage without. A super-low fat diet just isn’t healthy. And doesn’t it make sense intuitively that so many foods even vegans adore—nuts, seeds, avocados and coconuts—are high in fat?

Of course, eggs, fish, milk and plenty of other non-meat foods are also surprisingly high in fat—because we need it!

That’s why the whole fat-free movement is so ill-advised, and why fat-free vegan recipes are about as far off the reservation, nutritionally speaking, as it’s possible to go.

For instance: Scan most vegan recipes for baked goods and you’ll see that coconut milk is frequently specified as a substitute for cow’s milk. Why? Because it’s super high in saturated fat—about 87% of its total calories, to be exact. But you need that fat for flavor, mouthfeel and eating enjoyment.

If you’re vegan, however, you can wolf down your gluten-free donuts and pretend that coconut milk is oh-so superior to the real thing.

Finally, here’s a little calculation for the nutritionists, dieticians and vegans out there in love with the low-fat/fat-free diet concept. Suppose Person A eats 1,000 calories of carbohydrates (grains, fruits or veggies). At 4 calories per gram, they’ve consumed 250 grams of food, right?

Now, suppose Person B eats 1,000 calories from fat. At 9 calories per gram, that’s only 111 grams of food, so already Person A has taken in 139 grams more weight (since we’re talking weight loss here).

And biologically, water combines with ingested carbs at about a 4:1 ratio, which means that Person A ends up gaining over a kilogram of weight, versus Person B, who gained 111 grams. If you’re serious about weight loss, that’s a terrible comparison.

Which is why a low-fat/no-fat diet—ie, wholesale substitution of starch and veggies for fat—is absurd: Not only because it flies in the face of Nature, but because it doesn’t deliver weight loss.

For all its flawed thinking about preventing so-called animal abuse, a vegan diet is equally flawed in its assumptions about its effects on human health.

I don’t know which is worse, but you can take your pick: Either one by itself is a reason for rejection.

The opinions expressed in this commentary are solely those of Dan Murphy, a veteran food-industry journalist and commentator.