By Philip Blenkinsop

BRUSSELS (Reuters) - Belgian brewer InBev (INTB.BR: Quote, Profile, Research), the world's second-largest by volume, reported lower than expected first-quarter earnings as Brazilian beer sales fell and commodity costs rose, but it forecast a better second-half.

InBev shares, under pressure last week after downbeat comments at its shareholder meeting, were off 5.4 percent at 50.17 euros by 1335 GMT on Thursday compared with a DJ Stoxx European food and beverage index 0.3 percent higher.

The maker of Stella Artois and Beck's lager said EBITDA (earnings before interest, tax, depreciation and amortisation) was 982 million euros ($1.52 billion), against 962 million euros a year earlier, but only a like-for-like increase of 0.7 percent.

The average forecast in a Reuters poll of eight analysts was 1.06 billion euros.

InBev Chief Executive Carlos Brito blamed the tough first-quarter on a sharp 9.9 percent rise of the group's cost of sales, due largely to commodity price hikes, and also weak beer markets in two of its key areas, Brazil and Russia.

"We are confident that the Brazilian beer market will return to growth over the rest of the year," Brito told a briefing, and expected group EBITDA margins to rise in the second-half fuelled by further cost cutting after a first-quarter margin fall.

Cazenove analyst Matthew Webb summed up the results, "A weak set of figures with Brazil coming in well below expectations and pressure on costs across much of the business."

He added that the weaker market share performance in several key markets such as the UK, Russia and China mean that more reliable growth is available elsewhere amongst other brewers.