Lists of foods that "burn" belly flab are everywhere, and none of the foods on them does that alone. A better question is what happened when researchers changed what people ate and then measured the fat around their middle directly. Three diet trials did exactly that with nuts, green tea, a plant shake and a cut in red meat. This article walks through them and then puts dates next to the numbers.
This is general information, not personal medical or diet advice.
Walnuts in a Mediterranean-style lunch
The CENTRAL trial, run by researchers from Ben-Gurion University of the Negev in Israel, lasted 18 months at an isolated workplace where lunch was provided and monitored. It enrolled 278 inactive adults, three-quarters of them carrying excess fat around the abdomen; 89% were men and the average age was 48. One group followed a low-fat diet. The other ate a Mediterranean, lower-carbohydrate diet with 28g of walnuts a day, and the two diets had the same calories. Some people in each group were also given exercise, with a gym membership.
Weight loss ended up moderate and much the same on both diets. MRI scans told a different story. Visceral fat, the fat inside the abdomen, fell by 22% across the trial. People who exercised, on either diet, lost more of it than those who did not, even after allowing for weight loss. The Mediterranean group lost more fat from the liver and the pancreas than the low-fat group.
Those 28g of walnuts are not a free addition. USDA FoodData Central lists English walnuts at 654 kcal per 100g, so the daily handful comes to about 183 kcal. In the trial it was part of a diet matched in calories to the low-fat one.
Green tea, a duckweed shake and less red meat
The same research group followed this with DIRECT PLUS, another 18-month trial, with 294 people (88% men, average age 51). Everyone got physical activity. On top of that, one group followed standard healthy-eating guidelines, one a Mediterranean diet with 28g of walnuts a day, and one a "green" Mediterranean diet. The green group also drank 3–4 cups of green tea a day, had a shake made from 100g of frozen Wolffia globosa (a duckweed plant) a day, and ate less red meat.
The two Mediterranean groups lost similar weight (2.7% and 3.9%) and similar waist size (4.7% and 5.7%). Visceral fat did not follow that pattern. It fell 4.2% on the guidelines diet, 6.0% on the Mediterranean diet and 14.1% on the green version. More green tea, walnuts and duckweed, and less red meat, went with greater visceral fat loss. The study was funded by the California Walnuts Commission, which, the authors state, had no part in the design or the analysis.
Almonds in place of a muffin
The third trial was much smaller and shorter. At Pennsylvania State University, 48 adults ate a fully controlled diet for two six-week periods. In one period their daily snack was 1.5 ounces of almonds (about 42g); in the other it was a muffin with the same calories. Everything else stayed the same, and the main aim of the study was blood fats.
Body weight did not differ between the two periods. Abdominal fat was 0.07kg lower after the almond period, and leg fat 0.12kg lower. That is about 70 grams around the middle after six weeks, a real change but a very small one.
What the three trials have in common
None of them added a food on top of a normal diet and waited. Each swap happened inside a diet where calories were matched or controlled, and in the two Ben-Gurion trials exercise was part of the plan for at least some groups. The people studied were also mostly men in the two longer trials, so the results say less about women.
The NHS explains the basic rule behind this: "you're likely to lose weight if you eat and drink fewer calories than you use," because "your body uses its stored fat for energy." Nuts, tea or a green shake did not replace that rule in any of these trials. In DIRECT PLUS and the almond trial, what the food changes altered was how much of the fat lost came from the belly. In CENTRAL, the extra visceral fat loss came from exercise, and the walnut diet mainly cut liver and pancreas fat.
Where dates fit
None of the three trials used dates, so they say nothing about dates and belly fat either way. What can be said comes from food data. FoodData Central lists Medjool dates at 277 kcal, 66.5g of total sugars and 6.7g of fibre per 100g. Deglet Noor dates are listed at 282 kcal per 100g.
The NHS counts the sugar in whole fruit differently from added sugar: "sugar in fruit is not considered free sugars unless the fruit is juiced or puréed." Whole dates are on the whole-fruit side of that line. Date syrup and blended date drinks are not.
Portion size is the other part. The NHS says "a 30g portion of dried fruit, such as currants, dates, sultanas and figs, counts as 1 of your 5 A Day, but should be eaten at mealtimes, not as a snack between meals, to reduce the impact on teeth." Using the FoodData Central figure, 30g of Medjool dates comes to about 83 kcal, less than half the energy of the 28g walnut serving in the trials above. A few dates with a meal fits a calorie-controlled plan. A bowl of them on top of everything else does not.
More about this site is on the About Us page and the contact page.