If you want to lose weight, there seems to be only one way to do it: find an acceptable, nutritious diet that allows you to lower your calorie intake over the long term – and stick to it.  There is no magical macronutrient or food group that everyone can avoid or over-consume to reach their weight loss goals.
This was reminded after reading recent coverage of an unpublished meta-analysis showing that plant-based diets may help people with type 2 diabetes lose weight and reduce blood sugar levels. Little information about the research is currently available, although we can glean some details from press reports and comments from experts who reviewed the study poster presented at the European Congress on Obesity.
Despite the positive coverage the study received, it seems unlikely that avoiding animal products or loading up on plants led to the weight loss observed in the meta-analysis. It is possible that participants in the studies reviewed ate less than they had previously eaten, which led to their weight loss. So easy.
What do we know?
The researchers analyzed the results of 11 clinical trials involving 796 participants. These studies compared the effects of plant-based and control diets on heart disease-related risk factors including body weight, body mass index, blood sugar, blood pressure, total cholesterol, HDL, LDL, and triglycerides.
Unlike participants on a Mediterranean diet, those who followed a vegan program for three months lost just over nine pounds. Compared to a real control group that ate a “regular diet with no diet changes,” the vegetarian group lost an average of 16 pounds. The effect of the diet on total cholesterol, LDL, and blood sugar was very small.
Vegetarians were overjoyed
Unsurprisingly, the pro-vegan audience was impressed with the results. “The best way to lose weight for these patients, according to the Danish researchers, is to follow a plant-based diet,” Beet Contributor Maxwell Raab said of the meta-analysis. “The Danish researchers’ study will join an ever-growing body of research linking plant-based diets to weight loss and even improvement in diabetes symptoms.” Animal rights activists with the Physicians Committee for Responsible Medicine (PCRM) also reported that “plant foods help with weight loss and improve blood sugar.”
Lonnie is skeptical for several reasons, the most important of which comes from the reviewers themselves. According to the newspaper’s press release, all clinical trials had relatively small sample sizes, indicating that their results may not be generalizable. Perhaps most importantly, the macronutrient composition of plant-based diets “varied significantly”, and “none of the studies identified a control diet that completely matched the dietary intervention in all other respects except for the vegan diet”.
In other words, there is no way to know which aspects, if any, of a vegetarian diet promote weight loss. It may be that individuals assigned to a plant-based diet in these trials ate fewer calories than participants in the control groups. Of course, anyone can run into a calorie deficit whether they eat steaks or salads. Professor Ian Givens, Director of the Institute for Food, Nutrition and Health at the University of Reading, put it this way:
“…[A] The main question is whether the results of this study were due to a vegan diet or a reflection of lower energy intake, in other words the control meals were equal in energy… with vegan diets. This appears not to be the case as the authors note in their label conclusion “Some of this effect may contribute to differences in macronutrient composition and energy intake in vegetarian versus control diets.”
People lose weight when they follow strange diets
Does this mean that vegan diets are useless? No, I’m sure it works well for some people. But the fact remains: any diet can work, even if it’s really weird. For example, Duke University researcher Walter Kempner has helped thousands of people lose weight during his career by following a diet consisting of white rice, fruit, fruit juice, refined table sugar, and in some cases vitamin supplements. Just consider this Kempner madness published in JAMA in 1974:
“The patient takes an average of 250 to 350 g. From rice… All fruit and fruit juices are allowed, except for nuts, dates, avocados and any dried or canned fruit or fruit derivatives to which substances other than white sugar have been added. No more than one banana should be eaten per day. White sugar and dextrose can be used … On average, a patient takes about 100 grams per day, but if necessary, up to 500 grams per day should be used. Tomato and vegetable juices are not allowed.
If this system sounds psychotic to you, I sympathize with it. Sure, drinking fruit juice and white rice couldn’t fight obesity – except that it did. In 1975, Kempner and three colleagues published these findings in the Archives of Internal Medicine:
“One hundred and six severely obese patients, each of whom lost at least 45 kg, were treated as outpatients with the rice/reduction diet, exercise, and motivational reinforcements under daily supervision. The average weight loss was 63.9 kg [roughly 140 pounds]. “
Aside from the fact that today’s educators of fat acceptance will find Kempner’s language “problematic,” what can we learn from this paper? The prescribed diet was low in salt, low in fat, low in protein, and mostly cholesterol-free, coming in at less than 1,000 calories per day. A daily exercise plan was also described to the patients that pushed them “to their utmost tolerance of subjective comfort”. They were also allowed to reintegrate vegetables and meat over time.
I in no way endorse the Kempner approach, or any other diet method for that matter. What is clear, however, is that advocates promoting specific weight loss plans are generally effective for anyone and everyone is not working from good data. The unexciting conclusion we left is that reducing calories leads to weight loss. Eat animals or plants to your heart’s content. It doesn’t really matter – as long as you eat less.
 This is not advice to lose weight. Consult a doctor before following any diet.