NHS Evidence Health Information Resources formerly National Library for Health

Eating tomato ketchup daily reduces cholesterol levels reported five newspapers (6 December 2007). The reports were based on a small unrandomised trial which measured cholesterol levels of participants with normal cholesterol before and after a high tomato product diet, including ketchup. The reports were generally accurate, but the reliability of the study conclusions is unclear.

Five newspapers (1-5) reported on December 6th 2007 that tomato ketchup may help to reduce levels of cholesterol. Four of the papers reported that levels of low density lipoprotein (LDL) cholesterol fell by 13 percent (1-4), and three that levels of total cholesterol fell by 6 percent following a high tomato product diet (1,2, 4).
The reports were based on a non-randomised study of 21 people with normal cholesterol levels (6). Total and LDL cholesterol were measured at baseline, following a three week diet low in tomato products, and then following a three week high tomato diet of 30mg of tomato ketchup and 400ml tomato juice daily. The study found that both total cholesterol and LDL cholesterol were significantly lower (12.9% and 5.9% respectively) following the high tomato product diet compared to the low tomato product diet.
The newspapers were generally accurate in their reporting of the study. However three newspapers (1-3) reported that the subjects either consumed ketchup or tomato juice, and one referred only to ketchup (5), when both products were consumed by all participants. Three newspapers correctly reported that all volunteers had normal cholesterol levels when the study began (1,2,4). This study was small and unrandomised, and it is not clear how applicable the results would be to individuals with elevated levels of cholesterol.

Evaluation of the evidence base for intake of tomato products to decrease LDL cholesterol levels

Where does the evidence come from?

The research was carried out by a team from the University of Oulu, Finland, led by Dr Sohvi Hörkkö.

What were the authors' objectives?

The authors' objective was to investigate the effect on blood levels of total cholesterol and low density lipoprotein (LDL) cholesterol of a high tomato diet compared with a low tomato diet and a normal diet.

What was the nature of the evidence?

The evidence came from a non-randomised before-and-after study of 21 participants with baseline cholesterol levels in the normal range. The participants were healthy males and females aged 20 to 49 years, had a mean BMI of 23.5, and were all non-smokers. Total cholesterol and LDL were measured from overnight fasting blood samples at baseline, after the low tomato product diet and after the high tomato product diet. LDL oxidation and levels of carotene, lycopene, and vitamin C were also measured.

What interventions were examined in the research?

Two interventions were examined: a low tomato product diet and a high tomato product diet. After an initial baseline period of two weeks, each diet was followed for three consecutive weeks. For the low tomato diet, participants were instructed to follow their normal diet but to avoid tomatoes, tomato-based products, and other fruits or vegetables containing lycopene. The high tomato diet required participants to add 400ml tomato juice and 30g tomato ketchup daily to their normal diet.

What were the findings?

Mean plasma total cholesterol levels were lower following the high tomato diet compared to the low tomato diet (5.9% reduction) and to baseline (4.2% reduction). LDL cholesterol levels were also lower after the high tomato diet compared to the low tomato diet (12.9% reduction) and baseline (8.5% reduction). All these analyses were statistically significant. The authors state that these reductions in plasma cholesterol levels were not related to baseline levels, as all subjects showed a similar response. The study also found a significant decrease in LDL oxidation following the high tomato diet compared to baseline.

What were the authors' conclusions?

The authors concluded that a high dietary intake of tomato products significantly reduced LDL cholesterol levels and increased LDL resistance to oxidation in adults with normal cholesterol levels.

How reliable are the conclusions?

The conclusions are based on a small study which was unrandomised, and therefore they may not be reliable. They rely on comparing the levels of cholesterol in the same individuals at three different time points. This means that it is difficult to determine whether the intervention being examined is solely responsible for the change in cholesterol levels. In addition, the food intake of the participants was not monitored therefore it is unclear whether there were other dietary changes. As stated by the authors, larger controlled studies are required to establish the clinical benefits in people with elevated cholesterol levels.

Systematic reviews

Information staff at CRD searched for systematic reviews relevant to this topic. Systematic reviews are valuable sources of evidence as they locate, appraise and synthesize all available evidence on a particular topic.

There were no related systematic reviews identified on the Cochrane Database of Systematic Reviews (CDSR) and none on the Database of Abstracts of Reviews of Effects (DARE).