Thanks to my not-so secret network of "crazy diet finders" I get to hear stories like this:
"Overheard at the diner: 'On day three of my diet I get to have two 10 ounce pounds of any kind of meat I want, and three cold tomatoes.'" And apparently this diner repeated this info, more than once.
First of all, if you use phrases like "two 10 ounce pounds" you are probably having trouble losing weight because a) you are bad at math, or b) you are consuming too much alcohol at one sitting, or c) all of the above. Second of all, even though she was obviously trying to follow some form of a carb controlled and/or higher protein plan, I wasn't sure where the tomatoes were coming from. So I decided to do a little digging, and here's a summary of what I found:
1) Most of the "tomato diet" plans I saw assumed that people were not eating enough vegetables, period, and that people were filling in the gaps with high calorie/low nutrition processed grains. Basically, by adding sliced tomatoes to a meal, or making a homemade broth-based tomato soup to eat in between meals, people were filling up on lower calorie/higher nutrient dense foods, and that's what helped them lose weight. All fine and good, and convenient to a certain extent I suppose, but I think I would want to start throwing tomatoes out the window after a day or two. You should definitely let your meals overflow with non-starchy vegetables to fill up on all the fiber and water and get some good potassium, etc in the mean time, but you can certainly do that with more than just tomatoes. (And making a large batch of some kind of vegetable soup for freezing is a great convenient way to fill out a meal or snack.)
2) A second interesting tidbit was a claim that tomatoes suppressed appetite. I was able to trace this claim back to a small study done in the UK in 2009 where average weight women were fed a cream cheese sandwich either on carrot-enriched white bread or tomato-enriched white bread; apparently the women felt more "satisfied" after the tomato bread sandwiches. Some of the speculation involved was that the lycopene in the tomatoes might suppress ghrelin (which normally stimulates the appetite). First of all, the author of the study said "we need more research;" second of all, I wonder how many tomatoes it took to enrich those bread slices with lycopene. My experience with supplemental/enriched foods is that it usually takes a lot of one food to create a "therapeutic" level of a vitamin and/or mineral, so we might be looking at an impractical amount of tomatoes to eat or that we would actually have to "feed" a supplement manufacturer. So once again, if you want to "round out" your meal with tomatoes and other vegetables (try using lettuce leaves instead of bread as a lower calorie/nutrient dense substitute), and possibly get a longer lasting feeling of fullness, but there may not be anything magic about the tomatoes.
3) Of course no crazy diet would be complete without some mention of "detoxification." Go back and read this post if you are new to this blog or you just need a reminder that neither tomatoes nor anything else will improve your liver and/or kidney function and that "toxins" are the modern-day "evil spirits."
4) My favorite was probably one claim that tomatoes "activate your DNA" to help you shed fat. First of all, our friend Orac over at Respectful Insolence has already talked about this particular level of junk science, and the part about Jesus activating his DNA was particularly intriguing. All, I could say is, some of that DNA is junk for a reason and I probably don't want to activate it without knowing what the hell it's going to do. But anyway, it looks like the people making this claim were looking at a small study done in obese rats in which a substance called 13-oxo-ODA was derived from tomato juice and it seemed to reduce the amount of triglycerides in the blood and reduce the fatty deposits. This is interesting, but a) we can't extrapolate to humans although this is interesting, b) we don't if the substance acts the same while in it's tomato juice form, and c) there was no mention of weight loss, just that the triglycerides went down (which is a good thing, but there was no loss of body fat mentioned).
Take home message--you can use tomatoes and other non-starchy vegetables as a filler to increase satiety at meals and get more nutrition for less calories, but don't count on the tomatoes themselves to magically cause you to lose weight.