From Ergo Log
If you eat 300g raw tomatoes every day for a month, the concentration of HDL – the 'good cholesterol' – in your blood rises by 14 percent. Researchers at the Mexican Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran discovered this when they did a controlled medical trial.
It's more difficult to raise your HDL than it is to reduce your LDL. Stopping smoking, losing weight and intensive physical exercise all boost your HDL, but not necessarily by much. That's why the Mexicans' interest was piqued by scientific literature studies which showed that eating tomatoes boosted HDL levels. A healthy cholesterol balance is still the most important form of protection against cardiovascular disease known.
In 2003 epidemiologists at Harvard University discovered that women who ate tomato products more than seven times a week had thirty percent less chance of developing cardiovascular disease. [J Nutr. 2003 Jul;133(7):2336-41.]
When, nine years later, the same researchers re-examined the effects of a high tomato intake on cardiovascular health they discovered that tomatoes lowered the concentration of triglycerides, LDL and Haemoglobin A1c [glycated haemoglobin – higher concentrations of this can be an indication of disease] in the blood, but did not affect the HDL level. [J Nutr. 2012 Feb;142(2):326-33.]
The cardiovascular effects that the epidemiologists found were modest to say the least. This may be because many products that contain tomatoes – like pizzas and ketchup – are often part of an unhealthy lifestyle. Israeli researchers once performed an experiment in which subjects were given 300 g fresh – i.e. definitely not unhealthy – tomatoes to eat for a month. At the end of the experiment the amount of HDL in the subjects' blood had risen by 15.2 percent. [Clin Invest Med. 2006 Oct;29(5):298-300.]
The drawback was that the Israeli study did not have a control group. The Mexicans therefore decided to repeat the Israeli study, but with more methodological bells and whistles attached. They got together a group of about fifty subjects with low HDL cholesterol levels, but normal triglyceride concentration in their blood. They gave half of the subjects 300g Roma tomatoes every day; the other half were given 300g cucumber. Cucumber is not well endowed with bioactive substances.
At the end of the four weeks, the HDL level in the tomato group had risen by 14 percent, as the figure below shows. In the cucumber group there was no change.
The effect on the HDL level increased as the experiment progressed, as shown in the figure above.
According to doctors, for men a healthy blood HDL level is at least 40 mg per decilitre; for women the figure is at least 50 mg per decilitre. At the start of the experiment the subjects all had lower levels than these figures. Only two subjects achieved a healthy HDL level as a result of the tomato supplementation. This gives an indication of the size of the effect.
The researchers don't commit themselves to statements on the mechanism through which raw tomatoes might improve cholesterol levels. They suspect that lycopene [structural formula shown above], a carotenoid found in tomatoes, plays a role, but believe that other factors are also involved.
Diabetes Metab Syndr Obes. 2013 Jul 26;6:263-73.